Converting a string containing a function (t) to a useable variable.

I'm using inputdlg to take user input and calculate and store the value.

This is what I was trying to do.

x = inputdlg('Enter Mathematical Equation')

t = [0:0.001:20]

z = str2double (x{1})

I need to be able to enter 20*cos(4*t) for instance and have the calculated result stored in the variable, but I can't seem to get any result or for matlab to recognize the variable entered even if its declared prior to the inputdlg. Simply arguments like 20*cos(20) properly converts and calculates. How would I go on about being able to use the function from the string.

Answer 1

[dpb]

Need to convert string to the function---

>> t=0:pi/8:pi;            % predefined t
>> s='20*cos(4*t)';        % sample input string
>> s=vectorize(['@(t)' s]) % convert to allowable functional form and vectorize expression
s =
  '@(t)20.*cos(4.*t)'
>> fn=str2func(s)          % now create the function handle variable
fn =
function_handle with value:
  @(t)20.*cos(4.*t)
>>

>> z=fn(t)                % use it with existing t
z =
 20.0000    0.0000  -20.0000   -0.0000   20.0000    0.0000  -20.0000   -0.0000   20.0000
>> fn(0)                  % or with some other input, constant or variable ok...
ans =
  20
>>