How can I plot 3 signals using surf

I have three signals x1, x2 and x3 and I want to plot it in 3D surf plot

x1 = sort(Norm_Val(:,1)); x2 = sort(Norm_Val(:,2)); x3 = sort(Norm_Val(:,3)); mu = mean(Norm_Val); Sigma = cov(Norm_Val);

[X1,X2,X2] = meshgrid(x1,x2,x3); F = mvnpdf([X1(:) X2(:) X3(:)],mu,Sigma); F = reshape(F,length(x3),length(x2),length(x1)); %Size of F after reshape is 100*100*100 surf(x1,x2,F);

Kindly help me