Xdata for which Y's are calculated at each points are repeated according to Y(calc) e.g. Xdata=(x1,x2,x3....x1,x2,x3) Is this the right approach to the situation?
No, duplicating the Xdata is unnecessary and likely to cause errors. You should write your model function Ycalc=F(x,Xdata) so that it takes as input an Xdata matrix containing a single copy of all the x-values
Xdata=[x1,x2,x3,...xN]
and returns as output a matrix of all the y-values
Ycalc=[(y1calc(x1),y1calc(x2),y1calc(x3)
y2calc(x1),y2calc(x2)y2calc(x3)...]
The output Ycalc should be a matrix of the same size and shape as your Ydata input and the elements Ycalc(i) should be ordered such that you want Ycalc(i) to fit Ydata(i) as closely as possible. That is all that lsqcurvefit cares about.
