Operators

In DPUSER, operators are used to combine expressions. There are several types of operators:

Assignment

To assign a value to a variable, the assignment operator is used. The general syntax of an assignment is:
VARIABLE  = value
VARIABLE += value
...
or, if you wish to assign a value to a subset of a matrix:
VARIABLE[range]  = value
VARIABLE[range] += value
...
Like in the C programming language, several assignment operators are possible.
 
Operator Syntax Operands
Assignment VARIABLE = value Number, matrix, string, string array
Increment VARIABLE++ Number, matrix
Decrement VARIABLE-- Number, matrix
Multiplication VARIABLE *= value Number, matrix
Division VARIABLE /= value Number, matrix
Addition VARIABLE += value Number, matrix, string, string array
Subtraction VARIABLE -= value Number, matrix

If the "+=" operator is applied to a string array, the string at the right hand side of the statement will be appended to the string array.
The assignment operator "=" can be used to write a matrix as a FITS file. The syntax for doing this is 'filename'=matrix, i.e. you assign a matrix to a filename, which is in single quotes. Note that writing FITS files is also possible using the writefits procedure.

Examples

var = 6 creates a new variable named var and assigns a value of 6
'gauss.fits' = gauss(129, 129, 30) writes a 2-dimensional gaussian to a disk file named gauss.fits
var[100:200, *]++ Increments elements 100 through 200 in the first dimension and all elements in the second dimension

Parentesis

Parentesis are used in two ways: To enclose arguments to a function, and to group expressions. Parentesis can be used to override operator precedence.

Examples

print sin(pi()) prints out the sine of pi
var =  2 + 3  * 5  yields 17
var = (2 + 3) * 5 yields 25

Ranges

With ranges, you can create matrices and string arrays, and you can access subscripts of arrays. To access a single elements of a matrix, supply the coordinates like [5,3]. To access a range, give the inclusive range, separated by a colon like [100:300, 50:60]. You can use the asterisk (*) to access all elements in an axes. Ranges in DPUSER are 1-based like in fortran. The arguments in a range can be the result of an expression.

Examples

mvar = [1, sin(pi()), 3+5] creates a 1-dimensional matrix with the values 1, 0, 8
nvar = [-3600:3600] / 10 creates a 1D matrix with the values -360, -359.9, ..., 360
svar = ["test", "string"] creates a string array with 2 elements
print mvar[2] prints the second element of mvar, which is 0
print svar[1] prints out "test"
print svar[2][strlen(svar[2])] prints out the last character of the second element of svar, which is a "g"
newvar = nvar[3601:3700] creates a new matrix variable with 100 elements and assigns the values 0, 0.1, ..., 9.9

Mathematical operators

The basic mathematical operators are used in DPUSER. Depending on the type of associated variables, different actions (described below) are taken. If a matrix is combined with another matrix or a number, the result will be a matrix in which the operation is performed on each element. The available operators in precedence order are:
 
Operator Syntax Arguments Return Value
Exponentation x ^ y Number, Matrix Number if both x and y are numbers
Matrix if either x or y is a matrix
Multiplication x * y Number, Matrix Number if both x and y are numbers
Matrix if either x or y is a matrix
Matrix multiplication x # y Matrix or vector Matrix
Division x / y Number, Matrix Number if both x and y are numbers
Matrix if either x or y is a matrix
Modulus x % y Integer number Integer number
Addition x + y Number, Matrix Number if both x and y are numbers
Matrix if either x or y is a matrix
Number, String String if either x or y is a string
String, String array String array if either x or y is a string array
Subtraction x - y Number, Matrix Number if both x and y are numbers
Matrix if either x or y is a matrix

Boolean operators

Conditional statements can be given using the following operators. The list is in precedence order:
 
Operator Syntax Arguments Return Value
Not !x Boolean Boolean
Not equals x != y Number, String Boolean
Equals x == y Number, String Boolean
Greater than x > y Number, String Boolean
Greater or equal x >= y Number, String Boolean
Less than x < y Number, String Boolean
Less than or equal to x <= y Number, String Boolean
And x && y Boolean Boolean
Or x || y Boolean Boolean