# MATLAB: Do I get error for integral

MATLABmatlab integral

Hello,
I'm quite a matlab dummy and it would be nice, if you could help me with this.
When integrating the following function I get the error "Array indices must be positive integers or logical values.". I think it's about the "f(x)-u_equ(x))" term, which is negative. But as the formula is like this I don't know what to do. Sorry in advance if the question/solution is trivial.
``clear all;n=1;t1 = 14;t2 = 25;len = 20; %length of modelinitemp = 10; %initial temperaturesteps = 20;u_equ=zeros(1,steps);f=zeros(1,steps);% equilibrium temperaturefor x=1:steps    u_equ(x) = t1+((t2-t1)/len).*x;    f(x) = initemp;endfun = @(x) (f(x)-u_equ(x)).*sin((n.*pi.*x)/len);  %function to integrateintgr = integral(fun,0,len)``

``fun = @(x) (f-u_equ).*sin((n.*pi.*x)/len);  %function to integrate``
``intgr = integral(fun,0,len,'ArrayValued',1)``
``intgr =  -57.9324  -64.9352  -71.9380  -78.9409  -85.9437  -92.9465  -99.9493 -106.9521 -113.9549 -120.9578 -127.9606 -134.9634 -141.9662 -148.9690 -155.9718 -162.9747 -169.9775 -176.9803 -183.9831 -190.9859``