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HP50g  subset of a matrix  how to
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07082014 03:30 AM
Could somebody give an example how to extract a subset of a matrix, say extract a double column matrix from NxM matrix?
I have data in NxM matrix and want to perform approximation with LAGRANGE command, which needs a 2 column input data. For example from 3x4 matrix
1 1 1 2
2 4 8 4
3 9 27 6
extract columns 1 & 3, ie. get 3x2 matrix
1 1
2 8
3 27
Thanks
Re: HP50g  subset of a matrix  how to
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07082014 06:23 AM
I doubt this is the simplest way, but at least it works. Just put your matrix on the stack then do this:
DUP
{1 3} {3 3} SUB
{1 2} SWAP REPL
{1 1} {3 2} SUB
> [[1 1] [2 8] [3 27]] as requested.
For more information about the SUB and REPL commands, see the Advanced Users Reference Manual, pages 3242 and 3199, respecively. Other useful commands for column work are >COL, COL>, COL, and COL+ (pages 339 and 340).
Re: HP50g  subset of a matrix  how to
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07082014 03:52 PM
Thank you Joe. Your solution works. After a few tests I picked another way with CSWP command. For the special case above it would be something like
<< 2 3 CSWP {1 1} {3 2} SUB >>
In general it could be something like
<< > T I
<< T 2 I CSWP DUP
SIZE 1GET 2 2 >LIST
{1 1} SUB
>>
>>
Program takes 2 parameters: matrix T and column number I, then extracts two columns (1 and I) from T matrix. In column 1 are x'es, in other columns are values for approximation. The line with SIZE, GET and >LIST is to detetrmine number of rows of the matrix (I don't know simpler way :)
BTW, SCATRPLOT takes 2 columns from NxM matrix
Thank you for the hint.
Re: HP50g  subset of a matrix  how to
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07092014 08:44 AM
You can also use the COL command ( MTH MATRIX COL COL ).
Removes the desired column number from the matrix, returning new matrix and deleted column as a vector.
Here's a simple program.
Matrix is on Level 2 and a list of columns to delete is on level 1:
<<
SORT LIST> > n
<< n 1 + PICK
1 n FOR j
SWAP COL DROP
NEXT
>>
>>
So this:
returns this:
Note: I do not work for HP, I just like playing with calculators :)
Re: HP50g  subset of a matrix  how to
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07092014 11:10 PM
Here's another approach to Bart's program. Same inputs.
<< SORT REVLIST 1 << COL DROP >> DOLIST >>
Unlike Bart's program, however, this only returns the new (smaller) matrix; the original is lost.
Re: HP50g  subset of a matrix  how to
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07102014 04:15 AM
Joseph Horn wrote:<< SORT REVLIST 1 << COL DROP >> DOLIST >>
Brilliant solution Joe. I sometimes forget the 50g has recursive commands like DOLIST.
Joseph Horn wrote:Unlike Bart's program, however, this only returns the new (smaller) matrix; the original is lost.
That's because I used PICK instead of ROLL, but usually only the answer is required anyway  so your solution is "cleaner" :).
Note: I do not work for HP, I just like playing with calculators :)

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