why the value of 'k' is coming negative if all input values are positive

clc;
clear all;
close all;
syms x eta xi
x=0.577
y=[x x;x -x;-x x;-x -x]
jac=[0.25*(11+eta) 0.25*(1+xi);0.25*(-3-3*eta) 0.25*(9-3*xi)];
jacdet(xi,eta)=det(jac)
w1=1
w2=1

f(1)=0
for i=1:4
    xi=y(i,1)
    eta=y(i,2)
    m=eval(jacdet)
    psi1=0.25*(1-xi)*(1-eta)
    k=m*w1*w2*psi(1)
    f(1)=f(1)+k
    %f1=vpa(f1)
end

[James Tursa]

If all what input values are positive? I see negative numbers in several places in your code.

[David Goodmanson]

Hi Prateek,

w1,w2 >0; m (for your particular value of x) >0; psi(1) = -.5772