Introduction to Scilab

• Scilab is interpreted, not compiled

• Variables
  • no need to declare in advance -- in fact, can't declare
  • no need to specify type
  • can switch from one type to another
  • assign value with '='
  • if type name all by itself, with no semicolon, value printed to screen (in fact, this is true for any expression which doesn't end in semicolon)

• Workspace
  • save it with save filename
  • restore with load filename
  • record all commands typed with diary filename
  • stop recording with diary off

• Script files
  • place commands into a file mycommands.sci (the name doesn't have to end with .sci, but it may make the file easy to recognize)
  • type exec mycommands.sci, and everything is executed

• Arithmetic
  • standard operators + - * /
  • exponent operator ^
  • use parantheses to specify order of operations
  • there are no C-like ++ or +=

• Built-in Functions
  • lots and lots and lots of 'em -- see the section on elementary functions on the Scilab home page or just type help elementary for the basic math functions
  • all trig functions take arguments in radians (not degrees) (and no, pi is not pre-defined for you)
  • i is pre-defined to mean "square root of negative 1"; square roots of negative numbers yield complex results
  • type help foobar to get help on function "foobar"

• Printing values
  • Method 1: type the variable or expression without semicolon
  • Method 2: use the disp function
  • Method 3: for maximum flexibility, use mprintf (sends output to screen), mfprintf (sends output to a file) or msprintf (sends output to a string variable)
    • Example: print to screen: mprintf('value of a is %7.1f \n', a)
    • note that the format string (like all strings) is defined by single-quote (apostrophe) characters ', rather than by double-quote (quotation marks) characters "
    • Example: to print to a file,
      1. open the file: fid = mopen(filename, 'w')
      2. write to it: mfprintf(fid, 'string %s and integer %d\n', str, int)
      3. close the file: mclose(fid)

• Expressions -- for scalar quantities (vectors and matrices have their own set of functions), each of the following expressions will return T or F
  • equal to: a == b
  • not equal to: a ~= b
    this is not the same as the != comparison in C
  • greater than: a > b
  • less than: a < b
  • greater than or equal to: a >= b
  • less than or equal to: a <= b

• Control Flow
  • If

      if (a == b) then     if (a == b) then       if (a == b) then
        do this              do this                do this
      end                  else                   elseif (a > b)
                             do that                do that
                           end                    else
                                                    do the other thing
                                                  end
    

  • for

       for i = 1 : 10        for i = 1 : 0.1 : 2
         x = x + i;              x = sin(i);
       end                   end
    

    • note that the limits are inclusive at both ends, unlike C
    • note that if you include the increment, it falls in the middle of the for statement, unlike C

  • while

       while (i < 100)          while (i < 100) 
         do something             do something
       end                        if (result > i)
                                    break
                                  end
                               end
    

    • note that there is no "continue", like in C
    • the break command works in for loops, too

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.