Re: [newbie] prefered way to enter the values of a matrix interactively

[Ozzy Lash]

On Tue, Oct 16, 2012 at 2:36 PM, Juan Pablo Carbajal
<address@hidden> wrote:
> On Tue, Oct 16, 2012 at 9:18 PM, Jean Dubois <address@hidden> wrote:
>>
>>
>> 2012/10/16 Juan Pablo Carbajal <address@hidden>
>>>
>>> On Tue, Oct 16, 2012 at 9:04 PM, Jean Dubois <address@hidden>
>>> wrote:
>>> > What is the prefered way to enter the values of a matrix
>>> > interactively. I can imagine this is a common task which can be
>>> > performed by a predefined matlab-function and it probably is not a
>>> > good idea to try to program a function myself for this?
>>> > What I want is something like
>>> > enter matrix variable name
>>> > e.g. a
>>> > enter matrix dimension
>>> > e.g. 3
>>> > enter element 1,1
>>> > enter element 1,2
>>> > .
>>> > .
>>> > .enter element 3,3
>>> > a=...
>>> >
>>> > thanks in advance
>>> > _______________________________________________
>>> > Help-octave mailing list
>>> > address@hidden
>>> > https://mailman.cae.wisc.edu/listinfo/help-octave
>>> >
>>>
>>> Hi,
>>> I do not see the point of doing this in an interactive language, but
>>> anyways check function "input" and "eval"
>>>
>>>
>> Well to give you an example, I want a program which starts by asking the
>> user to enter two matrices a and b which will be later used for
>> demonstrating some kinds of matrix-operations in octave e.g. the difference
>> between a*b and a.*b just to name one example
>>
>> So, what you are telling me is to program it myself, I think I can do that
>> but I can't imagine I'm the first one who needs matrices to be entered
>> interactively therefore I was wondering whether there aren't any standard
>> functions available in Octave for this task.
>>
>> best regards,
>> jean
>>
>>
>
> Hi Jean,
>
> Please keep the mailing list always in copy.
>
> Octave is an interactive language, so you can enter a matrix directly
> from the command line
> A = [1 2; 3 4]
>
> Your program can ask the user to do that before running it. Lets say
> you have a script called lademo.m
> The user is running octave and executes your demo:
>
> octave:1> lademo
>
> If there isn't a matrix "A" defined then you can print a message asking for it
>
> if !exist ("A","var")
>  error("Please define the matrix 'A' before running this demo.\n")
> end
>
> This checks for the existence of a variable called "A" it will not
> check it size or contents. You can do that by adding checks, for
> example if it should be a numerical real array
> if !isreal (A)
>  # print a message
> end
>
> This is much easier than asking the user to introduce element by
> element and also simplifies your program by fixing the name of the
> matrix.
>
> Hope this helps
>
> Cheers
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://mailman.cae.wisc.edu/listinfo/help-octave

If I understand correctly, you might be able to do the following:

A=input("Enter values of A matrix, surrounded by [], with rows
separated by ; ");

(You may want to re-word the explanation, or describe the syntax once,
and ask for each input with less verbiage). When I type that into
ocatve I get:

octave:3> A=input("Enter values of A matrix, surrounded by [], with
rows separated by ; ");
Enter values of A matrix, surrounded by [], with rows separated by ; [
1 2 3; 4 5 6; 7 8 9]
octave:4> A
A =

   1   2   3
   4   5   6
   7   8   9