Unexpected result calculating the determinant of a singular matrix (42S)

10222019, 06:12 AM
Post: #20




RE: Unexpected result calculating the determinant of a singular matrix (42S)
Hi everyone.
The 48GX (and up) does not check whether the matrix elements are integer  it determines the least significant digit in the input (say it is of the order 10^s) and with Flag 54 clear it will round the result to 10^(s*n), with n the order of the matrix. (10212019 02:36 AM)Valentin Albillo Wrote: Try the 7x7 matrix I give as an example in the linked paper in the 48G and see if you get 1 as the determinant. You won't, the cheat doesn't work. ? of course the cheat works. With Flag 54 clear, the 48GX returns 1 exactly, with Flag 54 set it returns .999945522778. The condition number is about 10^11, and the 48GX works with 15 digits internally, so we get 1511=4 correct digts. Also, Valentin, the 42S uses a*bc*d when calculating the determinant of a 2x2 system, as you can see when you calculate the determinant of 1 2 3 1 and 1 2 0 3 1 0 0 0 1 The former returns 5 exactly, the latter 5.00000000001 Best Regards, Werner 

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