numerical integration dimension error

ok now Im getting another type of error

X = 0:1:100; Y = X.^(-1/2)*exp(-0.5*(0.00009996^2/X+34.3713^2*X)); Z =trapz(X,Y)
??? Error using ==> mldivide
Matrix dimensions must agree.

Whats wrong here? and how can I numerically integrate Y?

Answer 1

[Matt Fig]

You need a dot before every ^, * and / when working with vectors.

Y = X.^(-1/2).*exp(-0.5*(0.00009996^2./X+34.3713^2*X));

[john birt]

what do you mean?

X = 0:1:100; Y = X.^(-1/2).*exp(-0.5.*(0.00009996.^2./X+34.3713.^2.*X)); Z = trapz(X,Y)

is that correct as it produces Z = NAN which I was not expecting?

[Matt Fig]

You may not be expecting NAN, but that is how to make Y from X. Look at the exponent, it has values from -590 to -Inf. What do you think e^-590 is? ZERO (for all intents and purposes).

[john birt]

Thanks for your wisdom, I can get an answer if I change it to something like

X = 0.001:0.001:0.003; Y = X.^(-1/2).*exp(-0.5*(0.00009996^2./X+34.3713^2*X)); Z = trapz(X,Y)

Z = 0.0172

thanks again for your comments (dumb matlab coders like me need help!)