HP50g Algebraic matrix expressions

06262020, 04:38 AM
Post: #1




HP50g Algebraic matrix expressions
I usually do all my HP50 programming in RPL. And it has been a few years since I needed to do anything nontrivial.
But I have a need to use algebraic syntax for some complex expressions involving matrices, since the algebraic form is easier to verify visually for correctness. How do I refer to a single element of a matrix variable with an algebraic expression? "matrix1", "r", and "c" are all local variables in the current program fragment. I want to refer to the element in matrix1 at row r, column c. The obvious approach generates an error when I try to save from the command line: 'matrix1[r,c]'. This does not work. I have tried several obvious variations, but none of them work: 'matrix1[[r,c]]' 'matrix1[r c]' 'matrix1[[r c]]' Is what I am asking even possible with algebraic expressions? If so, what is the correct syntax? I have been unable to find any examples online of using subscripts for a matrix in an algebraic expression. Any pointers to such would be welcome! Thanks everyone! 

06262020, 06:17 AM
(This post was last modified: 06262020 03:36 PM by Giuseppe Donnini.)
Post: #2




RE: HP50g Algebraic matrix expressions
You are very close!
Just use parentheses: 'Matrix1(r,c)'. Think of it as a binary function which returns exactly one value. Like for any function, this works also for symbolic arguments, i.e. r and c can themselves be symbolic (variables or even expressions). 

06262020, 06:21 AM
Post: #3




RE: HP50g Algebraic matrix expressions
Thanks so much, Giuseppe!
Looks weird but it works. 

06262020, 06:31 AM
(This post was last modified: 06262020 06:37 AM by peacecalc.)
Post: #4




RE: HP50g Algebraic matrix expressions
Hello Sleazey,
Matrix is on Stacklevel 2 {row column} GET for example: \[ stacklevel ~~ 2: \left( \begin{array}{rrr} 1 & 2 & 3 \\ 4 & 5 & 6 \\ \end{array} \right)\] \[ stacklevel ~~ 1: \{ 2\quad 3 \} \] \[ command:\quad GET \] \[ returns: 6 \quad (element \quad second \quad row \quad third \quad column) \] For this approach your matrix doesn't need to be stored in variable. 

06262020, 06:33 AM
Post: #5




RE: HP50g Algebraic matrix expressions
Sure, but that's not what the original poster wanted!


06262020, 06:49 AM
Post: #6




RE: HP50g Algebraic matrix expressions
Hello Guiseppe,
sorry for posting something similar. I beg your pardon. I hope that wasn't too hard for you reading it. 

06262020, 07:32 AM
(This post was last modified: 06262020 03:37 PM by Giuseppe Donnini.)
Post: #7




RE: HP50g Algebraic matrix expressions
@peacecalc: I think you should calm down and stay ... peaceful.
In the interest of subsequent readers of this forum, I simply wanted to point out that your post doesn't address Sleazey's problem. Leaving it as the final answer to his question might suggest precisely that to a more casual reader. That's all. Warum immer gleich alles persĂ¶nlich nehmen? 

06262020, 02:56 PM
Post: #8




RE: HP50g Algebraic matrix expressions
To paraphrase Diego's signature line, "Read twice, post once"
Who decides? 

06262020, 04:07 PM
Post: #9




RE: HP50g Algebraic matrix expressions
FWIW, the GET command can also be used in Algebraic mode.
GET(matrix,{r,c}) It's not as nice looking as matrix(r,c), but GET can be used with a literal matrix. [[10,20][30,40]]>MM GET(MM,{2,2}) AND MM(2,2) both return 40. GET( [[10,20][30,40]],{2,2}) works but [[10,20][30,40]](2,2) does not. Likewise, GET(Ans(1),{2,2}) works but Ans(1)(2,2) does not. 

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