how to do differentiation?

Dear sir/madam,

I have a function y=f(x). I need to differentiate this function and find the value of the differentiation(slope) at a given point (x1,y1). How could I do this in matlab? Looking forward to hearing from you soon.

Thanking you, BSD

Answer 1

[Andrei Bobrov]

variant 1 use Symbolic Math Toolbox e.g.: your function f(x) = x^3+x^2*2+1

syms x
y = x^3+x^2*2+1;
df = matlabFunction(diff(y))
df = 
    @(x)x.*4.0+x.^2.*3.0
>> point = df(5)
point =
  95
>>

variant 2 use interpolation

x = linspace(-5,5,12);
y = x.^3+x.^2*2+1;
fpp = interp1(x,y,'pchip','pp')
dfpp = fnder(fpp)
df = @(x)fnval(dfpp,x)
point = df(5)

Answer 2

[Grzegorz Knor]

doc diff

[bsd]

diff() function performs only the differentiation.

After differentiating I also need the value at a given point (x1,y1).

BSD

Answer 3

[Walter Roberson]

subs() in the particular point values after doing the diff() .

If you need the value in the form of a double precision number instead of a symbolic number, then use double() on the result of the subs()

Answer 4

[Jakub Rysanek]

If you do not have access to Symbolic Math Toolbox, you may want to use one of my recent FileExchange submissions:

http://www.mathworks.com/matlabcentral/fileexchange/59438-symbolic-derivatives

Answer 5

[Francis Kamage]

f(x)=x^2-3*x+1

[Walter Roberson]

This does not appear to be an answer to the question that was asked?