Octave - Calculate argument in Symbolic function

The script convert symbolic expression df(x) to funtion dfh(x) using the

 function_handle Octave function. The script can run on Octave platform.
Download the file demo_sym.m

% Demo of how to use a number (which was calculated in an octave
% variable) in a symbolic calculation, without getting a warning.

% use octave to calculate some number:
 a = pi/2

% now do some work with the symbolic pkg
 syms x
 f = x * cos (x)
 df = diff (f)

% Now we want to evaluate df at a:

 % subs (df, x, a)     # this gives the "rats" warning (and gives a symbolic answer)

% So instead, try

 dfh = function_handle (df)

 disp('dfh(a) = ')
 dfh (a)

% ans = -1.5708


% And you can evaluate dfh at an array of "double" values:

disp ('dfh ([1.23 12.3 pi/2]) = ')
 dfh ([1.23 12.3 pi/2])

% ans =
%  -0.82502   4.20248  -1.57080

The Result

a =  1.5708
f = (sym) x*cos(x)
df = (sym) -x*sin(x) + cos(x)
dfh =

@(x)   -x .* sin (x) + cos (x)

dfh(a) =
ans = -1.5708
dfh ([1.23 12.3 pi/2]) =
ans =

  -0.82502   4.20248  -1.57080