Evaluate user input expression

Hi, I was wondering if there is a way to evaluate complicated user input expression If 'a' and 'b' are vectors and if user input is 'a*b' or 'a*b^2', how do I evaluate the expression?

Thanks, Rupa

Answer 1

[Walter Roberson]

If you read the expression as a string, then you can use symvar() to pull out the names of the variables the user used. You can then use exist() to test that each exists. Once you have done that, you can use vectorize() to convert * and / to .* and ./ . From there you could str2func and call that function passing in the values for the variables. Or you could eval()

Answer 2

[dpb]

>> a=1:3;
>> v=input('Enter Matlab vector expression for a: ')
Enter Matlab vector expression for a: a.^2
v =
   1     4     9
>>

Of course, this can be very dangerous...

[Rupamathi Jaddivada]

Is there a way I can check each term of the expression is defined in the code or not. For example, if user enters a.*b.*c and if b is not defined, can I display an error saying that 'b is not defined'?

[Image Analyst]

MATLAB will do that for you.