MaplePrimes - answers and comments on Question, dsolve/numeric otput-array

Example.

Jarekkk — Wed, 08 Feb 2012 17:43:54 Z

I created a simple example, just to show how it can be done:

s := 100:
F := dsolve({seq(diff(x[i](t), t) = x[i](t), i = 1 .. 6), seq(x[i](0) = i, i = 1 .. 6)}, numeric, 'output' = Array([seq(0.1*i, i = 1 .. s)]));

Then F[2, 1] is a matrix of calculated points (for all variables). For each variable to fit the function to it you have to extract two corresponding columns (of that matrix).

Extraction

ABond — Wed, 08 Feb 2012 18:14:29 Z

Thanks for the answer.

Basically I would like to know how to extract those data from the matrix F[2,1].

How one can do that?

Sorry for being not precise

I am sorry.

Jarekkk — Wed, 08 Feb 2012 21:03:48 Z

@ABond I am sorry I should have written this before. F[2,1] is a matrix containg 7 columns (first for the independent variable and others representing the dependent variables).

When you want the independet variable and the first dependent one (i.e. t and x[1](t)) - they are in the first two columns, so you can get them with:

F[2, 1][1 .. s, [1, 2]];

Then if you want e.g. t and x[2](t) (i.e. first and third column) you can type:

F[2, 1][1 .. s, [1, 3]];

and so on.

Edit: If you want to look at how you can extract chosen rows or columns from a Matrix (or a Vector), see ?LinearAlgebra/General/MVselect . In the example above I used the interval for the row index (which means all the rows in that interval) and the list for the column index, because I only wanted the listed columns.