MATLAB Expressions :: Basic Program Components (Programming)

Programming

MATLAB Expressions

Two specific types of MATLAB expressions covered in this section are

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/(m + n - 1)';
for m = 1:k
    for n = 1:k
        a(m,n) = eval(t);
    end
end

Here is 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 n = 1:10
    eval(['P', int2str(n), '= n .^ 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)

Operator Precedence Shell Escape Functions