Question

Hello I am new to MATLAB , I wanted to know how can I make my string into function . I want to access the function as a string from user in standard Matlab format (e.g exp(-10*X)-sin(pi*X)-2*tanh(X) ) Here X is the variable. Then I want to replace ‘X’ with ‘low’ and ‘high’ variables to calculate value of function at these limits. I have used ‘strrep’ for this purpose. I am getting the following errors
1)Undefined function or variable ‘X’.
2) I cannot see whether ‘X’ was replaced with ‘low’ and ‘high’.

Any help will be truly appreciated.
Below is my code.

    high=input('Upper Limit of the Interval : ');

    low=input('\nLower Limit of the interval : ');

    usr_funct=input('Enter The Function in standard Matlab Format.\nEnter "X" for the
    variable and * for multiply \n');    % Example exp(-10*X)-sin(pi*X)-2*tanh(X);

    middle = (low+high)/2;

    Flow =strrep(usr_funct, 'X', 'low');
    Fhigh =strrep(usr_funct, 'X', 'high');

   sprintf('Flow '); % This was to check if 'X' was replaced with 'low'. It is not printing anything

Answer 1

I think that you are looking for the eval function. That will evaluate a string as matlab code.

Here is an example:

str = 'exp(-10*X)-sin(pi*X)-2*tanh(X)' ; % let str be your math expression
high = 10; % Ask the user
low = -5; % Ask the user

% Now we evaluate for High and Low
X = low; % We want to evaluate for low
ResultLow = eval(str); % That will return your value for X = low
X = high; % We want to evaluate for low
ResultHigh = eval(str); % That will return your value for X = high