[edit: I changed the comments in the code for t1 and t. I added a line to display the fitted values.]
load('sinusoidal');
[rows,cols]=size(Sinusoidal); % read data form file
t1=(1:rows)'; % t1=vector
t=repmat(t1,1,cols); % t=array
Sinusoidal=reshape(Sinusoidal,rows*cols,1); % convert array to vector
T=Sinusoidal(~isnan(Sinusoidal)); % remove NaNs
t=t(~isnan(Sinusoidal)); % remove corresponding times
% next: define the model equation
myfittype=fittype('a*sin(w*t+p)','dependent',{'T'},'independent',{'t'},'coefficients',{'a','w','p'});
x0=[30,.1,0]; % initial guess for [a,b,c]
myfit=fit(t,T,myfittype,'StartPoint',x0); % fit the data
plot(myfit,'-b',t,T,'r.'); % plot results
xlabel('Time'); ylabel('Temperature')
% Display best-fit parameters on console.
fprintf('y=a*sin(wt+p): a=%.4f, w=%.4f, p=%.4f\n',myfit.a,myfit.w,myfit.p)
Try it.
