In MATLAB:

Using the X and Y values below, write a MATLAB function SECOND_DERIV in MATLAB. The output of the function should be the approximate value for the second derivative of the data at x, the input variable of the function. Use the forward difference method and interpolate to get your final answer. X=[1,1.2,1.44,1.73,2.07,2.49,2.99,3.58,4.3,5.16,6.19,7.43,8.92,10.7,12.84,15.41,18.49];

Y=[18.89,19.25,19.83,20.71,21.96,23.6,25.56,27.52,28.67,27.2,19.38,-2.05,-50.9,-152.82,-354.73,-741.48,-1465.11];?

This is my coding:

function output = SECOND_DERIV(R)

X=[1,1.2,1.44,1.73,2.07,2.49,2.99,3.58,4.3,5.16,6.19,7.43,8.92,10.7,12.84,15.41,18.49]; Y=[18.89,19.25,19.83,20.71,21.96,23.6,25.56,27.52,28.67,27.2,19.38,-2.05,-50.9,-152.82,-354.73,-741.48,-1465.11];

%forward difference method first time XX=X(1:end-1)

%first derivative dydx=diff(Y)./diff(X)

%second derivative dydx2=diff(dydx)

%forward difference method second time XXX=XX(1:end-1)

%get the second derivative from input x output= interp1(XXX,dydx2,x,'linear','extrap')

end

I do not know what wrong with it.