Diff () function

[bbarker]

I am a student, and we have put together a small script to calculate the roots of an equation using newton raphson itteration in Matlab - all well and good. However, I decided it would be nice if you could change the function from the terminal, rather than changing the code each time you wanted to solve a new problem.

The problem is, the way most people will enter an equation is in symbolic notation (e.g x^2 +3). On top of this, I need to differentiate my function, (i.e obtain 2x from the above). The diff function will do this, but only (it seems) if fed a symbolic equation.

However, I need the equation in the form
x.^2 +3 - note the x. for element operations - or else my program fails spectacularly

Is there any way I can convert from symbolic notation to this?

Thanks

Ben

 

[joe3]

Hi,
Just convert it to non-symbolic array:
>> X=sym(magic(4))

X = % symbolic input

[ 16, 2, 3, 13]
[ 5, 11, 10, 8]
[ 9, 7, 6, 12]
[ 4, 14, 15, 1]
>> z=double(X) % get ride of symbolic properties

z =

16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1

>> d=diff(z.^2-1)

d =

-231 117 91 -105
56 -72 -64 80
-65 147 189 -143
D=sym(d) % If you need a symbolic result


D =

[ -231, 117, 91, -105]
[ 56, -72, -64, 80]
[ -65, 147, 189, -143]