Why do I have this error when I try to derivative a function with variable x?

I dont know why i have this error. Please help me.

This is my code:

function [dX,s,x,o,dU,B] = fcn( nref,dnref,ddnref,e1,de1, u)

lamda1 = [15.6 10.6;10.6 10.4];

s = de1+ lamda1*e1;

g1 = 5;

g2 = 1;

g3 = 1;

n = nref-e1;

dn = dnref+lamda1*e1-s;

x = [e1';s'];

M = [g1+2*g2*cos(n(2)) g3+g2*cos(n(2));g3+g2*cos(n(2)) g3];

C = [-g2*sin(n(2))*dn(2) -g2*sin(n(2))*(dn(1)+dn(2));g2*sin(n(2))*dn(1) 0];

Y = -M^-1*C*s;

A = [-lamda1*e1+s;Y;dnref;ddnref];

b1 = zeros(2,2);

b2 = zeros(4,2);

B = [b1;M^-1;b2];

dX = A+B*u;

U = [x(1)^2;x(1)*x(2);x(2)^2;x(3)^2;x(3)^2*cos(n(2));x(3)*x(4);x(3)*x(4)*cos(n(2));x(4)^2];

o = diff(U,x)*dX;

dU = diff(U,x);

Coder error: Difference order N must be a positive integer scalar in the range 1 to intmax('coder.internal.indexInt') in 'o' function.

Answer 1

[Sulaymon Eshkabilov]

Hi,

here you are trying to compute numerical differentiation and thus, you need to use these commands:

     o = (diff(U)./diff(x))*dX;
    dU = diff(U)./diff(x);    

Should you want to get symbolic differentiation, then you'd need introduce symbolic variables, e.g.:

    syms U(x)
    dU = diff(U(x), x)
    ddU = diff(dU, x)
    ...

[chuyen hoangcao]

Wow, thank you so much for helping me answer the question. The numerical differentiation is not wrong, but in matlab function block it does not support for symbolic differentiation with syms U(x). Maybe I will use the numerical differentiation.