Create a matrix

01262019, 11:19 AM
Post: #1




Create a matrix
Specifically, I would like to create a matrix, using a 3 element specified pattern, (tridiagonal), with a specified number of rows and columns. The center value of the pattern should be on the main diagonal of the matrix:
Some kind of variation on this (nonworking) theme: makemat([1,2,1], 5,5); // Uses the pattern 1,2,1 in a 5x5 matrix, with 2 on the main diagonal: [[2,1,0,0,0], [1,2,1,0,0], [0,1,2,1,0], [0,0,1,2,1], [0,0,0,1,2]] I (think) this can be done using the matlab eye() command, for example. Any ideas how to create a custom matrix in similar fashion, on the prime? Dale 

01262019, 12:00 PM
(This post was last modified: 01262019 12:37 PM by JMB.)
Post: #2




RE: Create a matrix
Try:
MAKEMAT(IFTE(I=J,2,IFTE(J=I1 OR J=I+1,1,0)),5,5) Or: MAKEMAT(IFTE(I=J,2,IFTE(ABS(IJ)=1,1,0)),5,5) Josep Mollera. HP PRIME, HW: C, SW: 2.1.14425 (2020 01 16). 

01262019, 03:18 PM
Post: #3




RE: Create a matrix
Thank you for your suggestions!
Something interesting happens when I copy from your post, into the [CAS] (emulator): MAKEMAT(IFTE(I=J,2,IFTE(J=I1 OR J=I+1,1,0)),5,5) : CAS changed changed all of the IFTE()'s to when()'s: MAKEMAT(when(I=J,2,when(J=I1 OR J=I+1,1,0)),5,5) Then I recalled that result to the command line, it changed all of the when()'s to: MAKEMAT(((I = J)? 2 : (((J = (I1)) OR (J = (I+1)))? 1 : 0)),5,5) I've never seen that last format before, on the prime. Maybe an XCAS shorthand? 

01262019, 05:49 PM
(This post was last modified: 01262019 05:50 PM by JMB.)
Post: #4




RE: Create a matrix
The programming language C has this same ternary operator
Cond ? a : b If Cond is true returns a, otherwise returns b. https://en.wikipedia.org/wiki/%3F: Josep Mollera. HP PRIME, HW: C, SW: 2.1.14425 (2020 01 16). 

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