I am more than dumb ... but may I be excused for being such an amateur? Not! Haha. So, I thought I could use the Ldoor matrix directly after stripping off the headers. That part I got right. But I failed to realize in order to use the SparseConvertFromCoordinate I was required to adjust the coordinate format row and column number from 1, 1 to 0, 0 , and, of course, for all subsequent coordinate format rows and columns. I updated the original code with this part of code which reduces coordinate numbers by 1. And everything ran! Well, at least I got some answers and exit code 0. // assign forced unwrapping for casting to appropriate arrays for index in 0...rowcountm1 { rows32[index] = Int32(rows![index] - 1 ) cols32[index] = Int32(cols![index] - 1 ) datsdouble[index] = Double(dats![index]) }

I re-tested on the 4x4 example given in Apple documentation on Creating a Sparse Matrix from Coordinate Format Arrays. Adjusted all the coordinates up by 1 and ran with the code with the - 1 to reduce the coordinate rows and columns coordinates just to be sure. Everything works (answers are correct). So, I just have to remember when downloading to check the coordinates to see where they start, and adjust if need be.