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DRAFT Specifications of the

Dictionary Relational Expression Language dREL:

 

Syd Hall, Doug du Boulay, Ian R. Castleden, and Nick Spadaccini

 

1. Purpose and Function

The primary purpose of the dictionary relational expression language, dREL, is to enable relationships between data items in a dictionary to be specified, simply and succinctly, as a symbolic methods script written in dREL. The facility to derive data values from other items provides a powerful approach for precisely defining data and mitigates against the need to archive derivable tertiary data, and much of the secondary data - as these can now be calculated from the primary data present in data files.

The definition example in Fig 1 shows how dREL methods are used. This definition contains the attribute _method.expression which specifies, in dREL, the crystallographic unit cell volume as a function of the cell lengths and angles.

save_cell.volume

_definition.id '_cell.volume'

_description.text

;

Volume of the crystal unit cell.

;

_name.category_id cell

_name.object_id volume

_type.container Single

_type.contents Real

_type.purpose Measurement

_enumeration.range 0.0:

_units.code angstroms_cubed

_method.expression

;

With v as cell_vector

_cell.volume = v.a * ( v.b ^ v.c )

;

save_

Figure 1: Definition of the crystal cell volume.

The evaluation process works as follows, assuming that a data file is being read with a search utility that uses associated domain dictionaries for validation and checking support. If the item _cell.volume is requested but its value is not present in the file, the utility automatically transfers the script from _method.expression to a dREL handler. This parses the script, identifies the length and angle items needed to evaluate the cell volume, requests these values from the data file, and calculates the volume. The evaluation process assumes that any data item referenced not in the data file will itself be derived from a methods expression. The dREL parser will recursively derive data values as needed, until either the required items are found or calculated, or the relationship pathways are exhausted. The calculated cell volume is passed back to the utility, which responds identically to the request as if the value had been present in the data file.

This example shows that methods expressions in the dictionaries provide a clarity and precision not achievable in the past. The use of methods, with the coalescence of dictionaries, will promote an exploitation of data well beyond that achievable in the past. For example it would mean that only primitive data need be archived in data files, and the related data can be derived when needed using algorithms contained in the dictionary. This would reduce the amount of data that needs to be exchanged and archived. Some derived quantities (e.g. atomic coordinates), may continue to be archived, but, having the methods definitions in associated dictionaries, specifying precisely how they were derived, will enable new derivations to be evaluated as better approaches are developed.

 

2. Primitive Data Types

dREL supports the following primitive data types:

 

2.1 Character Strings

Character strings are created in two ways; explicitly from dictionary definitions of the object, or implicitly from usage in an expression.

2.1.1 Dictionary definition

The DDL dictionary definitions declare the TYPE of data using _type.contents

2.1.2 Inline definition

Character strings are created by enclosing a string in quoting literals. Matching single and double quote characters at the extremities of a single line string implicitly identify a literal object as TYPE CHARACTER. Matching triple quote characters at the extremities of a multi-line string implicitly identify a literal object as TYPE CHARACTER.

2.1.2.1 Single quotes

Matching single quote characters at the extremities of a single line string implicitly identify a literal object as TYPE character. The following is simple character string.

'single quotes make it easy to embed a "double quote"'

2.1.2.2 Double quotes

Matching double quote characters at the extremities of a single line string implicitly identify a literal object as TYPE character. The following is simple character string.

"double quotes make it easy to embed a 'single quote'"

It is also possible to use C-style elides to achieve this effect.

"double quotes don't prevent the use of a \"double quote\""

2.1.2.3 Triple quotes

Matching triple quote characters at the extremities of a multi-line string implicitly identify a literal object as TYPE character. The following is simple character string.

""" triple quotes

are

multi-line"""

This is equivalent to

"triple quotes\nare\nmulti line\n"

Triple quotes comprised of the single quote literal are also supported.

'''single or double quotes are can be

used to define the triple quote sequence.'''

2.1.2.4 Special explicit strings

dREL provides for two special string literal definitions; raw and Unicode strings.

A raw string is delimited by r"... ". Characters in a raw string are interpreted literally and regular expressions or sequences of characters are protected from parser interpretation. Here is an example.

r"raw quotes don't interpret escapes viz:\n << not a newline!"

This is equivalent to the following string.

"raw quotes don't interpret escapes viz:\\n << not a newline!"

 

2.2 Integer Numbers

dREL supports decimal, binary, octal and hexadecimal Integer numbers. These are identified in three ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

2.2.1 Dictionary definition

The DDL dictionary definitions declare the TYPE of data using _type.contents.

2.2.2 Inline definition

2.2.2.1 Decimal integers

The syntax of a decimal integer is: [+-]?[0-9]+

An example decimal integer is: -23

2.2.2.2 Binary integers

The syntax of a binary integer is: [0][bB][0-1]+

An example binary integer is: 0b1101110010111000

2.2.2.3 Octal integers

The syntax of a octal integer is: [0][oO][0-7]+

An example octal integer is: 0o63103

2.2.2.4 Hexadecimal integers

The syntax of a hexadecimal integer is: [0][xX][0-9a-fA-F]+

An example hexadecimal integer is: 0x6672af

 

2.3 Real Numbers

dREL supports decimal and scientific Real (or floating-point) objects. Real numbers are identified in three ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

2.3.1 Dictionary definition

The DDL dictionary definitions declare the TYPE of data using _type.contents.

2.3.2 Inline definition

3.3.2.1 Decimal real numbers

The syntax of a decimal real number is: [+-]? ([0-9]+.[0-9]* | .[0-9]+) [Ee][+-]?[0-9]+

An example decimal real number is: -7893.8221 or -7.89382e+3

2.3.3 Explicit definition

Conversion to real number is achieved with the function:

 

2.4 Complex Numbers

dREL supports Complex number objects. Complex numbers are identified in three ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

2.4.1 Dictionary definition

The DDL dictionary definitions declare the TYPE of data using _type.contents.

2.4.2 Inline definition

2.4.2.1 Complex numbers

The syntax of a complex number is: ((Real|DecimalInteger) [+-])? (Real|DecimalInteger) [j J]

An example complex number is: -7893.8221+54.924j

2.4.3 Explicit definition

Conversion to a complex number is achieved with the function:

 

2.5 Measured Numbers

A Measured value consists of a number and its standard uncertainty appended in parentheses. The uncertainty value is an integer scaled to the precision of the last digits of the measurement value. Measurement numbers are identified in three ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

2.5.1 Dictionary definition

The dictionary definitions declare the TYPE of a data object with the following set of attribute declarations:

 

_type.contents Real

_type.purpose Measured

The value of the attribute _type.contents can also be Integer or Complex.

2.5.2 Inline definition

3.5.2.1 Measured numbers

The syntax of a measurement number is: [Real|DecimalInteger]\([1-9][0-9]*\)

An example measurement number is: -783.2(12) = -783.2±1.2

Other examples are x.xxE-yy(zz) or x.xx(zz)E-yy or x.xxE-yy(z.zzE+ww) where a '.' in the standard uncertainty value indicates an explicit value.

2.5.3 Explicit definition

Conversion to a measurement number is achieved with the function:

 

3. Container Types for dREL

 

dREL supports the container types

dREL also supports the nesting of container types i.e. the definition

_item.container Tuple[Tuple]

_item_dimension [5[3]]

refers to a list of five tuples containing three elements.

 

3.1 List Containers

List containers are mutable objects with the following properties.

Type: contained items may be of any, but the same, TYPE.

Dimension: Lists are single dimensioned.

Size: the length of a table is not pre-defined.

Access: indexed by integers.

Shape: may be nested.

Lists are created in three ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

3.1.1 Dictionary definition

The dictionary definitions declare the nature of a List container with attribute declarations. Here are such declarations for a list of real numbers of nine elements.

_type.container List

_type.contents Real

_type.dimension [9]

3.1.2 Inline definition

Lists may be defined inline using the List(...) function. E.g.

List ([1, 2, 3, 4])

 

3.2 Tuple Containers

Tuple containers are immutable objects with the following properties.

Type: items may be of any TYPE.

Dimension: are single dimensioned.

Size: needs to be defined.

Access: indexed by integers.

Shape: may be nested.

Tuples are created in three ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

3.2.1 Dictionary definition

The dictionary definitions declare the nature of a Tuple container with attribute declarations. Here are such declarations for a tuple of three values.

_type.container Tuple

_type.dimension [3]

3.2.2 Inline definition

Tuples may be defined inline using the Tuple(...) function. E.g.

Tuple (10.2, 12.3, 7.4)

Tuple ('a', 'b', 'static')

 

3.3 Table Containers

Table containers are similar to Lists except that each value in the table may have an associated key. A table has the following properties.

Tables are created in two ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

 

3.3.1 Dictionary definition

The dictionary definitions identify a Table object with the following attribute declarations.

_type.container Table

_type.contents Real

A Table differs from a List (see §3.1) in several important ways. A List object contains a specified number of values that are identified explicitly by sequence. A Table contains a sequence of character or number values which identified by a key.

3.3.2 Explicit definition

Conversion of a sequence of objects to a new list is achieved with the function:

Table ('left':'links', 'right':'recht')

 

3.4. Array Containers

Array containers are immutable objects with the following properties.

Arrays are created in two ways; explicitly from dictionary definitions of the object, implicitly from usage in the expression language, or explicitly using a function.

3.4.1 Dictionary definition

The dictionary definitions declare the nature of an array with attribute declarations. Here are the attributes for defining a three element integer vector, indexed from 0 to 2.

_type.container Array

_type.contents Integer

_type.dimension [3]

3.4.2 Inline definition

Vectors may be defined inline using the Vector(....) function. E.g.

Array ([10.2, 12.3, 7.4])

 

 

4. Language Basics

 

In this section the basic syntax of dREL, and the language elements that lead up to controlling the execution flow, are introduced. It is important to appreciate that dREL does not support, or require, data declarations other than those already discussed in §3. Nor does it provide, in this version at least, input/output control statements.

 

4.1 Assignment Expressions

4.1.1 Named objects

A NAMED object or 'variable' in dREL may only be created on assignment (see §4.1.2), The typing of a variable is by coersion (see §4.1.3 and §4.2). The scope of a variable is local.

4.1.2 Assignment statement

The process of object transfer is initiated with the '=' character which transfers the value of the right-hand expression of objects Robjects to the left-hand objects Lobjects. The general form of the object transfer is:

Lobjects = Robjects

In the example below the value of the literal Integer object, '5', is assigned to a mutable NAME object, the variable string 'x'.

x = 5

Robjects may also be an expression of objects.

x = y * z

y = Sin (a) + Cos (a)

Multiple transfers are also allowed.

a, b, c = 3.628, -7.67, 5.329

4.1.3 Assignment TYPE

In dREL, object types are not declared. We have already seen in §3, the typing of Robjects items may be determined from dictionary definitions, inline typing constructions or simply inferred by association with objects of known type. The TYPE of Lobjects may be set by the same mechanisms, or result directly from the inferred type of the Robjects value.

It follows that the statement

x = 5

sets the TYPE of 'x' as Integer. A new assignment of 'x' in the next statement

x = 10

is permitted because it has a consistent TYPE. However, the assignment

x = "Hello World"

is illegal but will not cause an error message to be raised.

This is contrary to the practice of some scripting languages, but it avoids the faulty and misleading construction of expressions.

 

4.2 TYPE Coercion Rules

Type coercion rules are needed when Robjects expressions contain objects of mixed type. dREL uses the following coercion rule, in order of increasing priority.

Integer Real Complex

In the next statement, Lobjects is of type Real, provided this is the first assignment to "x".

x = 5 + 7/2

 

4.3 Comments

Comments are non-executable strings. In dREL a sequence of characters following an unquoted sharp or hash symbol # is interpreted as a comment, up to the end-of-line character. Here are typical examples.

x = 5 # a comment follows an in-line hash

The following statement does not contain a comment because the hash symbol is contained within a quoted string.

s = "# this is *not* a comment"

 

4.4 Expression Operators and Terminators

dREL supports the following arithmetic expression operators

+ add

* multiply

** power

- subtract

/ divide

The operands apply to Integer, Real and Complex number objects. They are also applicable to the containers List, Tuple, Table, Vector and Matrix provided the elements of these are of TYPE number. The expression operators + and * have meaning for manipulating character strings.

dREL supports the following logical expression operators

== equals

!= not equals

>= greater than or equals

<= less than or equals

and and

or or

in matches element of the list

not in does not matches element of the list

 

dREL supports the following expression terminators

; semicolon separates multiple expressions in a line

\n newline closes a line unless a balancing ')', '}' or ']' is missing

Example statements using these terminators follow.

a = 234 ; y = 45 ; z = -2

b = (y + z)/2.0

c = (45 + 72 *

(93 + 4) + z)

 

4.5 Supported Escape Sequences

The following special character sequences are supported in dREL expressions. Note that the same diagraphs may be used for other purposes in data values, but within the literal dREL scripts the following meanings will be assumed.

\n newline

\r carriage return

\f formfeed

\t horizontal tab

\b binary bit pattern # implements backspace!

\o octal bit pattern # try \0xxx instead

\x hexadecimal bit pattern

\0 null character

\\ backslash (\)

\u Unicode character in hexadecimal E.g. \u0022 == '

Note that a Unicode character in a string makes the entire string of TYPE Unicode.

 

 

5. Flow Control

 

dREL supports a range of standard and specialised flow control statements and terminators for controlling the repeated execution of object expressions. These are as follows:

The essential constituents of a repetitive execution sequence, is as follows.

repeat-statement {

*expression block*

repeat-terminator (optional)

}

If more than one expression exists within the expression block, it MUST be enclosed within a set of braces "{" and "}". If only one expression is repeated, its association with the repeat_statement is implied and the braces are optional. In general, it is good and safe programming practice to always use braces to bound the repeated expression block.

 

5.1 DO STATEMENT

Indexed repetition of expressions is supplied with a Do statement.

Do index = first, last, incr { *expression block* }

The index variable is initialised with the first index value (or variable) and executes the expression block provided index is less than or equal to the last index value (or variable). The index is incremented by the incr value AFTER each execution of the expression block. The incr value is option and has a default value of 1.

A typical application of the Do operator follows.

Do i = 0,20,2 { total = total + subtotal[i]; }

 

5.2 FOR STATEMENT

Manipulation of List items is provided with with a For statement.

For a in list : n op m { * expression block * }

where a is the current element of the entire list. An optional expression ':n op m' is available to control the accessing of list packets, where n is the index (starting at 0) for each packet; op is the test operator (< > <= >= allowed) and m is the test integer operand. The op and m entries are optional. The index n is a local variable and may be tested elsewhere in the script.

An example where list is a literal object follows.

i = 0

For a in ['Mon','Tues','Wednes','Thurs','Fri'] {

Day[i] = a + "day"; i += 1; }

 

5.3 LOOP STATEMENT

A fundamental function of dREL is to apply and derive data in a data file using definitions in a dictionary. Much of this data is in looped lists, and, consequently, there needs to be a simple and transparent way to identify and apply repetitive data items. Data items in the same list are, according to the dictionary language DDL3, classified as belonging to the same generic category group. The id code of a category is therefore a convenient tag to identify groups of items, and to access 'packets' (i.e. sub-lists) of data items in lists. The Loop repetition operator is provided primarily for this purpose.

Loop local as list : n op m { * expression block * }

The string local is an object variable, local only to the specific methods script in which it is invoked, which assumes the successive values of list during the repeated execution of an expression block. If list is a category id code, then the local object contains successive sub-list of tagged values (i.e. an implicit Table) and individual data items may be accessed as object attributes of local. An optional expression ':n op m' is available to control the looping of list packets, where n is the loop index (starting at 0) for each packet; op is the test operator (< > <= >= allowed) and m is the test integer operand. The op and m entries are optional. The index n is a local variable and may be tested elsewhere in the script.

 

5.3.1 Data Loop Example 1

A simple invocation of Loop will now be considered for data. This example will access two data items in the category POSITION, known by their data names as _position.vector_xyz and _position.object_id. An abbreviated definition of the category and these items follow. Note that _position.object_id is specified as the category key to each packet of these items.

_category.id position

_category_key.index_id '_position.object_id'

 

_definition.id '_position.number'

_name.category_id position

_name.object_id number

_type.container Single

_type.contents Integer

_type.purpose Index

 

_definition.id '_position.object_id'

_name.category_id position

_name.object_id object_id

_type.container Single

_type.contents Uchar

 

_definition.id '_position.vector_xyz'

_name.category_id position

_name.object_id vector_xyz

_type.container Array

_type.contents Real

_type.dimension [3]

 

In a data file these items might appear in a looped list (abbreviated) as follows.

loop_

_position.object_id

_position.number

_position.vector_xyz

1 origin [0.0, 0.0, 0.0]

2 body-diagonal [5.0, 5.0, 5.0]

32 diagonal-terminal [10.0, 10.0, 10.0]

In a dREL script the Loop construct allows individual items in a packet (in this instance the packet contains three values) to be addressed by the extension name defined in the dictionary with the attribute _item.extension (i.e. number, object_id and vector_xyz).

Loop a as position {

If (a.object_id == "origin") {

CoordOrigin = a.vector_xyz }

Else LocalPosn[a.number] = a.vector_xyz

}

 

5.3.2 Data Loop Example 2

Another example is needed to illustrate the functionality of the Loop operator when handling lists of data from non-hierarchically-related but derived, categories. The prototype dictionary language allows hierarchical relationships between data items to be defined, via category definitions, and these provide access "pathways" which are independent of how these related data are stored in the data file. For instance, items in the same category, or in hierarchically-related categories, may be accessed as an attribute extension of either the name of the 'parent' category (i.e. the highest category in the family hierarchy) or the name of the hierarchically-related category.

All data in a looped list be of the same category family. Items from hierarchically-related categories may be in more than one looped list but for the purposes of access, the dREL parser subsumes these items into a common list.

However, categories of data which are derived from another category will often use category keys which refer to the same quanities. In these cases, the keys are not implicitly equivalent (as would be the case if the categories were hierarchically related) but they are 'linked' using the DDL attribute _name.parent_item_id. Here is the definition of an item in the category GEOM which is linked to a category key in the category POSITION (see Example 1).

_definition.id '_geom.vertex1_id'

_name.category_id geom

_name.object_id vertex1_id

_name.linked_item_id '_position.object_id'

_type.container Single

_type.contents Uchar

The _name.linked_item_id attribute specify that _geom.vertex1_id has a value that is common to one of the unique values of the item _position.object_id. This linkage implies that _position.object_id is a "key" unique item in the category POSITION. The same relationships also apply for the items _geom.vertex2_id and _geom.vertex3_id, which are shown below in an example data list.

loop_

_geom.type

_geom.vertex1_id

_geom.vertex2_id

_geom.vertex3_id

point origin . .

line origin body-diagonal .

line body-diagonal diagonal-terminal .

triangle origin body-diagonal diagonal-terminal

As in §5.3.2, specific values in this list can be accessed via their unique extension names. However, because of the defined relationship between the vertex ID's and the _position.object_id (in Example 1), these can be used to 'point' to specific packets and items in the POSITION category using the <category>[<key>].<extension> construction. The With command is described in the next section.

With p as position

Loop g as geom {

If (g.type == "point") {

PointList += Tuple([g.vertex1_id,p[vertex1_id].vector_xyz])

}

Else if (g.type == "line") {

LineList += Tuple( [Tuple ([g.vertex1_id, g.vertex2_id],

Tuple ([p[g.vertex1_id].vector_xyz,

p[g.vertex2_id].vector_xyz])])

}}

This illustrates how values from the category list can be directly accessed simply by appending the name extensions to the item which is linked to the key of that list. The value of LineList[1]is [["origin","body-diagonal"],[[0.0,0.0,0.0],[5.0,5.0,5.0]]]

 

5.4 WITH Statement

The With statement is identical to the Loop statement except that the list pointer is not incremented. This statement is used only to identify the current list object within scope and context as a local object. The general form is as follows.

With local as list { *expression block* }

This statement is very useful for accessing data items in the current packet of a category lists. This enables items in a list to be addressed as name extension attributes, just as in Loop.

With p as atom_site

If (label == p.id) x = p.frac_vector

 

Note the braces about the expression block are required for multiline expressions.

 

5.5 WHERE STATEMENT

The Where operator is used to test all elements in arrays or lists, which may be of indeterminate length. This operator has the general form:

Where (expr) { *expression block* }

Else { *expression block* }

If A and B are arrays of the same shape then the statement works element by element.

Where (A>0) { B = 1.0/A }

Else { B = large }

It is difficult to write an equivalent statement to this using other operators because the shape of arrays (e.g. the number of dimensions) might be unknown.

 

5.6 BREAK Terminator

Repetitive blocks can be exited prematurely with the Break keyword. The general form of the statement is as follows.

Break

For example, in the sequence

Do i=1:10 {

Do j=i+1:10 {

If (a[i] < a[j]) Break

}}

 

5.7 NEXT Terminator

Repetitive blocks can be reset prematurely with the Next keyword. The general form of the statement is as follows.

Next

For example, in the sequence

Do i=1:10 {

Do j=i+1:10 {

If (a[i] < a[j]) Next

}}

 

5.8 IF/ELSEIF/ELSE Statements

The standard If/ElseIf/Else statements have the following form and sequence. The If statement must precede all others in the sequence. The Else statement must, if used, follow all others. There may be any number of ElseIf statements.

If (expr) { *expression block* }

Else If (expr) { *expression block* }

Else { *expression block* }

Braces around the expression blocks are necessary if they contain more than one statement.

 

5.9 SWITCH/CASE/DEFAULT Statements

The Switch statements are used to execute expression blocks according to a match with an enumerated value. The operators have the general form:

Switch (var) { ## lowercase 'switch' may work

Case (val1,.., valN) { *expression block* } ## case

Case (valM,.., valQ) { *expression block* }

Default { *expression block* } ## default

}

where var is the variable NAMED object whose value is tested against values val1,.., valQ. When there is a match, the corresponding expression block is entered. NOTE that all case lists are tested and more than one expression block may be entered. If no case blocks are entered, the default block is entered.

Here is an example of a Switch sequence of statements.

Switch (NUM) {

Case (5) { .... }

Case (7,8,6) { ..... }

Case (1:4) {...... }

Default { ..... } }

The case labels must be constant expressions.

 

6. Intrinsic Functions

 

dREL has an extensive set of intrinsic functions, which are listed in this section according to the following classes.

 

6.1 CONVERSION and MANIPULATION Functions.

These functions are responsible for fixing the TYPE of the contained object.

Complex() Convert two arguments (Real, Imag) into a Complex number

Real(), Imag() Returns real and imaginary part of Complex argument

Integer() Convert argument into an integer number

Float(), Rem() Convert to real number, get remainder of real number

Int(), Nint() Convert to trucated integer, rounded-up integer value

List() Convert arguments into a List object.

Tuple() Convert arguments into a Tuple object.

Table() Convert arguments into a Table object.

Vector() Convert arguments into a Vector object.

Matrix() Convert arguments into a Matrix object.

Array() Convert arguments into an List, Vector or Matrix object.

Numb() Convert the character argument into the ascii number equivalent.

Char() Convert the ascii number argument into a character equivalent.

Minor() Generate a matrix of minor elements from the matrix argument.

Cofactor() Generate a matrix of cofactor elements from the matrix argument.

Adjoint() Generate a matrix of adjoint elements from the matrix argument.

Inverse() Generate a matrix of inverse elements from the matrix argument.

Transpose() Generate a matrix of transposed elements from the matrix argument.

Eigen() Get eigenvalues and vectors of a 3x3 matrix and return as three tuples

containing four elements (value plus vector of direction cosines).

 

6.2 TRIGONOMETRIC Functions.

These functions are responsible for performing trigonometric operations on the argument.

Sin(), Cos(), Tan() Sine, cosine and tangent functions of radian arguments.

Sind(), Cosd(), Tand() Sine, cosine and tangent functions of degree arguments.

Asin(), Acos(), Atan() Arcsine, cosine and tangent functions as radians.

Arcsin(), Arccos(), Arctan() Arcsine, cosine and tangent functions as radians.

Asind(), Acosd(), Atand() Arcsine, cosine and tangent functions as degrees.

Atan2(a,b), Atan2d(a,b) Arctangent function in radians and degrees

Phase() Get the phase in radians for a Complex number.

Exp(), ExpIm(), ExpImag() Exponential functions with Real and Complex arguments.

Log(), Ln() Base-10 and natural logarithm functions.

Pi, TwoPi Values of p and 2p.

 

6.3 MATHEMATICAL Functions

These functions are responsible for performing mathematical operations on the arguments.

Sqrt() Get square root of number.

Mod() Modulus of arg1 to base arg2.

Abs(), Magn() Absolute value of the argument.

Sign() Sign of argment 2 applied to argument 1.

Sum() Sum all of all the values in the list object.

First(), Last() Get the first and last element of a list or character string.

Strip(list, n) Strip the nth element from the list. (n=0,1,2...)

Len() Get the length of a list or character string.

Map(list,func) Apply the function func to each element in the list. ## no function defs

Sort() Sort all elements in a list from small to large.

Sort(list, func) Sort the list according to the function func. ## no function defs

Reverse() Reverse the order of a list.

TopLo(), TopHi() Sort all elements in a list from small to large; large to small.

Dim() Return an integer list of dimension lengths. Zero value is end of array.

Det() Get the determinant of a matrix

Dot(), Cross() Scalar and vector product of two vectors.

Norm() Root mean square value of elements in a list or vector.

MaxI(list,ind) Maximum value in list. Index of max value returned as argument 2.

MinI(list,ind) Minimum value in list. Index of max value returned as argument 2.

Max(), Min() Maximum and minimum values in the list.

SubString(s1, s2) Returns TRUE if string s1 is a substring of s2.

Eigen(mat) Return sorted list of three (value, vector) tuples.

 

6.3 DISCIPLINE Functions

In the Crystallographic CORE dictionary the following functions are defined.

AtomType() Extract the 'atom_type' element symbol from a character string.

Closest(v, u) Returns [w, t ] where w is the closest real space vector transformation of v to

u, and t is the integer cell vector that converts v to w.

SeitzFromJones() Converts each x,y,z symop into a 4x4 Seitz matrix.

SymEquiv(s,c,xyz) Converts the input factional xyz vector into a vector transformed by the

symop s in the symmetry_equiv category name c.

SymLat() Convert the symop code n_jkl into a lattice vector [j-5, k-5, l-5]

SymNum() Convert the symop code n_jkl into a symmetry integer n. (n=0,1,2...)

Symop(index, lvect) Convert symmetry equivalent position number index and cell lattice vector

lvect to the symop code n_jkl. (n=1,2,3...)

 

7. List Operators

 

7.1 String Concatenation

The following properties of strings apply.

 

7.1.1 Concatenation of literals

Multiple sequential string literals will be concatenated automatically in statements. E.g.

x = "string literals that are adjacent" " are concatenated"

equivalent to

x = "string literals that are adjacent are concatenated"

 

7.1.2 Concatenation of objects

The operators + and * may be applied to string objects. Here is an example of the + operator.

s1 = "this" ; s2 = " and that"

s3 = s1 + s2

The object s3 now holds 'this and that'.

Strings made up of multiple instances of the same character sequence can be generated by the * operator, as below.

s4 = "-"*10

The object s4 now holds a string "-----------". The * operator can be applied to named objects as well.

s4 = "-EOF-" ; s5 = s4*3

The object s4 now holds a string "-EOF--EOF--EOF-".

 

7.2 List Membership

It is possible to test objects containing lists of strings for the 'membership' of specific strings. These tests are equivalent to looping through the lists and applying the standard string equivalence operators '==' and '!=', as illustrated in the following example statements.

cnt = List(["data_", "global_", "save_", "stop_", "loop_"])

Do i=0,4 { If('stop_' == cnt[i]) Break ;}

The last statement is problematical because the length of the list of items being tested needs to be known. It may be replaced simply by:

If ('stop_' in cnt) { ... }

This works only if elements of the container are of the same type. The negation test for membership of a list also applies. E.g.

If ('cell_' not in cnt) { ... }

 

7.3 List Notation

The following notation is available for the formation of lists from existing named lists.

new = list[:] New copy of entire list.

new = list[n:m:i] New list with elements from indices n to m in steps of i.

new = list[n:m] New list of elements from indices n to m in steps of 1.

new = list[first+1:last-1] New list without the first and last elements. #not implemented

val = list[1] Extract a single value.

new = list1 + list2 New list of list1 concatenated with list2.

new = [list1, list2] New list of list1 concatenated with list2.

list1 ++= val Append val to list1.

list[i:j] = list2 Cut and paste ALL of list2 into the elements i to j-1.

new = list!n New list composed of n copies of list.

new = n*list New list with list elements multiplied by a number n.

E.g. 10*[1,2,3] results in [10,20,30];

3*["a","b","c"] results in ["aaa","bbb","ccc"].

new = x+list New list made from list with value x added to all elements

E.g. 10+[1,2,3] results in [11,12,13]

3+["a","b","c"] results in ["3a","3b","3c"].

list = list + x Add value x to all elements of an existing list.

 

7.4 Array Notation

The following notation applies strictly to Vector and Matrix objects.

var = mat[n,m] Variable contains the value of the matrix element (n,m)

mat[p,q] = x Matrix element (p,q) is replace with the value of x. #Its immutable

vec = mat[:,j] Vector formed from jth column of row matrix elements. # mat.v[:j]

vec = mat[first:last-1,k] Vector formed from kth column of row elements first to last-1.

vec = vec1 + val Scalar addition. [9,10,11] = Vector([4,5,6]) + 5

vec = Function(vec1) Vector function. [1,2,0] = Mod([4,5,6], 3) for (Mod, Int, )

vec = vec1 + vec2 Vector addition. [12,14,16] = Vector([4,5,6]) + Vector([8,9,10])

var = vec1 * vec2 Scalar (dot) product. 8*4+9*5+10*6 =Vector([4,5,6])*Vector([8,9,10])

vec = vec1 ^ vec2 Vector (cross) product. (-4,8,-4) = Vector([4,5,6]) ^ Vector([8,9,10])

vec = mat * vec1 Post-matrix vector multiply.

E.g. [32,77,112] = Matrix([[1,2,3],[4,5,6],[7,8,9]]) * Vector([4,5,6])

vec = vec1 * mat Pre-matrix vector multiply.

E.g. [66,81,96] = Vector([4,5,6]) * Matrix([[1,2,3],[4,5,6],[7,8,9]])

mat = mat1 * mat2 Matrix multiply. Matrices must have concordant shapes.


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