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HP-50g Algebraic matrix expressions - Sleazey - 06-26-2020 04:38 AM
I usually do all my HP50 programming in RPL. And it has been a few years since I needed to do anything non-trivial.
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!
RE: HP-50g Algebraic matrix expressions - Giuseppe Donnini - 06-26-2020 06:17 AM
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).
RE: HP-50g Algebraic matrix expressions - Sleazey - 06-26-2020 06:21 AM
Thanks so much, Giuseppe!
Looks weird but it works.
RE: HP-50g Algebraic matrix expressions - peacecalc - 06-26-2020 06:31 AM
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.
RE: HP-50g Algebraic matrix expressions - Giuseppe Donnini - 06-26-2020 06:33 AM
Sure, but that's not what the original poster wanted!
RE: HP-50g Algebraic matrix expressions - peacecalc - 06-26-2020 06:49 AM
Hello Guiseppe,
sorry for posting something similar. I beg your pardon. I hope that wasn't too hard for you reading it.
RE: HP-50g Algebraic matrix expressions - Giuseppe Donnini - 06-26-2020 07:32 AM
@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 persönlich nehmen?
RE: HP-50g Algebraic matrix expressions - mfleming - 06-26-2020 02:56 PM
To paraphrase Diego's signature line, "Read twice, post once"
RE: HP-50g Algebraic matrix expressions - Wes Loewer - 06-26-2020 04:07 PM
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.