Evaluate user input expression

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Rupamathi Jaddivada
回答： Walter Roberson 2017-1-15
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

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回答（2 个）

Walter Roberson
Walter Roberson 2017-1-15
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()
dpb
dpb 2017-1-14
>> 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...
  2 个评论
Rupamathi Jaddivada
Rupamathi Jaddivada 2017-1-15
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
Image Analyst 2017-1-15
MATLAB will do that for you.

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