how to calculate derivative of a string

dear all

i have a problem with calculating the derivative of a aglebraic expression which is string. how can i use diff to calculate the derivative of expression?

the problem is as below:

eq='x^2+x';
f=str2func(['@(x)',eq]);
g=diff(f);

thanks alot

Answer 1

[madhan ravi]

eq='x^2+x';
f = sym(str2func(['@(x)',eq]));
g = diff(f)

[madhan ravi]

Or try:

eq='x^2+x';
f = sym(eq);
diff(f)

[saeed rezaei]

thank you so much

it works! :)

now i wanna use the g and calculate different values. for example i wanna calculate g(2), but it doesn't work. because g is a symbol. now, how can i change the g to a function?

[madhan ravi]

g = matlabFunction(diff(f));
g(2)

[saeed rezaei]

thanks alot bro

it works!

[Ashesh Choudhury]

Thank you so much. You are a saviour. @madhan

Answer 2

[Guillaume]

Replace your str2func, by str2sym to create a symbolic expression:

eq='x^2+x';
f = str2sym(eq);
g = diff(f);

[saeed rezaei]

thank you for your help

but, it seems that str2sym function doesn't work in matlab R2015a.

do you have any other suggestion ?