Programming and Data Types

String Evaluation

String evaluation adds power and flexibility to the MATLAB language, letting you perform operations like executing user-supplied strings and constructing executable strings through concatenation of strings stored in variables.

eval

The eval function evaluates a string that contains a MATLAB expression, statement, or function call. In its simplest form, the eval syntax is

• eval('string')
  

For example, this code uses eval on an expression to generate a Hilbert matrix of order n.

• t = '1/(i+j-1)';
  for i = 1:n
      for j = 1:n
          a(i,j) = eval(t);
      end
  end
  

Here's an example that uses eval on a statement.

• eval('t = clock');
  

Constructing Strings for Evaluation

You can concatenate strings to create a complete expression for input to eval. This code shows how eval can create 10 variables named P1, P2, ...P10, and set each of them to a different value.

• for i=1:10
      eval(['P',int2str(i),'= i.^2'])
  end
  

feval

The feval function differs from eval in that it executes a function rather than a MATLAB expression. The function to be executed is specified in the first argument by either a function handle or a string containing the function name.

You can use feval and the input function to choose one of several tasks defined by M-files. This example uses function handles for the sin, cos, and log functions.

• fun = [@sin; @cos; @log];
  k = input('Choose function number: ');
  x = input('Enter value: ');
  feval(fun(k),x)
  

Note    Use feval rather than eval whenever possible. M-files that use feval execute faster and can be compiled with the MATLAB Compiler.

return

Dates and Times