Hi there! i have this function handle: integrando= @(x,landa,t) 1-exp(-((1/(landa*t))*((exp(-landa*x)/x)+((x-x0).*(1+landa*x0)-x0)*(exp(-landa*x0)/(x0^2))))); which as you can see using fplot(@(x) integrando(x,3,0.00063),[0 1.1225]) its value is constant (actually 1, and then starts decreasing exponentially until drops to zero at 1.1225). Landa and t are parameters that change the curvature of this drop. Since this is a positive and finite function, I'm waiting a positive integral. However, integrating this same function on this same interval, I get negative figures! >> q1=integral(@(x) integrando(x,3,0.00063),0,1.1225) q1 = -20.3981 This is getting me nuts! I would very much appreciate any help. Thanks in advance!