Numerical differentiation.

dydx = deriv(y)
dydx = deriv(x,y)

This function computes the first derivative of the vector or matrix y and returns it in dydx, which has the same size as y. If y is a matrix, differentiation occurs along columns. If the abscissa x is not supplied, it is assumed to be 1:length(y) for vectors and 1:size(y,1) for matrices.

There is a caveat about using deriv. A numerical derivative is computed by taking differences of adjacent elements in y. So it is save to use deriv for smooth signals, but it gives very noisy derivative for noisy signals. In such a case, it is much better to apply a simultaneous smoothing/differentiation using the function datasmooth.

To compute the first derivative of a sin function

x = linspace(0,5*pi,1001);
y = sin(x);
dydx = deriv(x,y);
plot(x,y,'k',x,dydx,'g');
legend('original function','derivative');

datasmooth