MATLAB: How to calculate a derivative of function numerically

derivativefunctionMATLABnumerical

I have a continuous function of two variables:
f = @(x,y) x.^2 + (y-1).^2
How do I calculate a derivative of this function numerically? I tried two different ways and got errors:
% First try
df = @(x,y) diff(f(x,y),x)
df(1,2)
ans = []
% Second try
df = @(x,y) diff(f,x)
df(1,2)
Undefined function 'diff' for input arguments of type 'function_handle'
I must not set the derivative separately.

Best Answer

A numerical differentiation means a variation of the argument and a quotient of the differences:
df = (f(x + h) - f(x)) / h           % one sided
df = (f(x + h) - f(x - h)) / (2*h)   % two sided
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