how to do differentiation?

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bsd on 6 Sep 2011
Commented: Walter Roberson on 16 May 2021
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

Accepted Answer

Andrei Bobrov
Andrei Bobrov on 6 Sep 2011
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 =
>> point = df(5)
point =
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)

More Answers (4)

Grzegorz Knor
Grzegorz Knor on 6 Sep 2011
doc diff
  1 Comment
bsd on 6 Sep 2011
diff() function performs only the differentiation.
After differentiating I also need the value at a given point (x1,y1).

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Walter Roberson
Walter Roberson on 6 Sep 2011
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()

Jakub Rysanek
Jakub Rysanek on 4 Oct 2016
If you do not have access to Symbolic Math Toolbox, you may want to use one of my recent FileExchange submissions:

Francis Kamage
Francis Kamage on 16 May 2021
  1 Comment
Walter Roberson
Walter Roberson on 16 May 2021
This does not appear to be an answer to the question that was asked?

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