Problem with derivative function

Hello, I have a problem with dfunc(x) which is my derivative function. The problem is that when using derivative we have to use symbolic value but I want dfunc(x) to actually return f'(x) which is a numerical result.I tried to use subs but it would give me answers like 2*2^(1/2) - (2*exp(1/2))/(exp(1/2) - 1)^2 instead of the actual numerical value. How can I solve it?

[Stephen23]

"How can I solve it?"

Look at the list of functions in the symbolic toolbox:

https://www.mathworks.com/help/symbolic/referencelist.html?type=function&s_tid=CRUX_topnav

particularly under the title "Conversion Between Symbolic and Numeric", e.g.:

https://www.mathworks.com/help/symbolic/double.html

https://www.mathworks.com/help/symbolic/vpa.html

Answer 1

[John D'Errico]

What you don't seem to appreciate is that in the eyes of the symbolic toolbox, something like 2^(-1/2) Is a numerical result. Sort of. Yes, I suppose the difference is a subtle one. There are no unknown parameters in there.

What you want is a floating point result. For that you can use a tool like VPA to turn the result into a symbolic floating point number, so a high precision float.

X = str2sym('2^(-1/2)')

X = 

vpa(X)

ans = 

0.70710678118654752440084436210485

Or you can use double, which converts the result into a double precision float.

format long g
double(X)

ans = 
         0.707106781186548