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 Original Message (ID '436877') By Bill Simpson: In Response To 'Re: Re: Re: Re: Help with creating matrix from ...' --------- One possible source of errors is the order of x,y in a[[x,y]] or a[[y,x]]. This In[1]:= m = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; m[[1, 2]] Out[2]= 2 shows that 1,2 is first row, second column and not first column, second row. Thus it is m[[y,x]] or m[[row,column]] if you think of x being horizontal across the screen from left to right and y being vertical from the top of the screen to the bottom. This problem can also appear with Table[expr,{x,1,3},{y,1,3}] instead of Table[expr,{y,1,3},{x,1,3}]. I realize I can sometimes not be careful with this and make errors when calculating with data that expects x and y ordering. Please see if this might be a source of the error and when you provide me with the examples I will also check this possible error and correct it.