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[Garth Wells <question112556@xxxxxxxxxxxxxxxxxxxxx>]

Question #112556 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/112556

    Status: Open => Answered

Garth Wells proposed the following answer:
On May 28 2010, Phil Marinier wrote:

>New question #112556 on DOLFIN:
>https://answers.launchpad.net/dolfin/+question/112556
>
> I am attempting to use LinearSolver in C++ to do some simple matrix and 
> vector solution, as in 3x3 or 5x5. I get this error.
>
>
> [0]PETSC ERROR: --------------------- Error Message 
> ------------------------------------ [0]PETSC ERROR: Object is in wrong 
> state! [0]PETSC ERROR: Not for unassembled matrix! [0]PETSC ERROR: 
> ------------------------------------------------------------------------ 
> [0]PETSC ERROR: Petsc Release Version 3.0.0, Patch 8, Fri Aug 21 14:02:12 
> CDT 2009
>
>
> This seems to suggest that I cannot use LinearSolver in the code 
> directly, that instead I have to make a form file. Is this in fact the 
> case? and if so how would I make that form file?
>

You need to call A.apply(), X.apply(), etc before using the matrix and 
vectors.

Manipulating small matrices using sparse linear algebra objects will be 
dead slow. I would recommend using Armadillo (take a look in 
dolfin/adaptivity for an example).

Garth


>
> This is my code in case it is relevant. I am doing some simple 
> interpolation to calculate a step size for an iterative non-linear 
> problem. This is the test program I wrote.
>
>
>int main()
>{
>	//declare and initialise
>	int degree = 4;
>	double *x = new double[degree + 1];
>	double *y = new double[degree + 1];
>	
>	std::vector<dolfin::uint> columns;
>	std::vector<double> values;
>	
>	dolfin::LinearSolver linSolver;
>	dolfin::Matrix X(degree + 1, degree + 1);
>	dolfin::Vector Y(degree + 1);
>	dolfin::Vector A(degree + 1);
>	
>	//generate test points
>	x[0] = 0;
>	y[0] = 0;
>	
>	x[1] = 1;
>	y[1] = -2;
>	
>	x[2] = 2;
>	y[2] = -1;
>	
>	x[3] = 3;
>	y[3] = -2;
>	
>	x[4] = 4;
>	y[4] = 0;
>	
>	
>	//set vector
>	Y.set_local(y);
>	
>	//set matrix
>	for (int j = 0; j <= degree; j ++)
>		columns.push_back(dolfin::uint(j));
>	
>	for (dolfin::uint row = 0; row < dolfin::uint(degree); row++){
>		
>		for (int j = 0; j <= degree; j++)
>			values.push_back( power(x[row], (degree - j) ) );
>		
>		X.setrow(row, columns, values);
>		
>		values.clear();
>	}
>	
>	//solve [X]{A} = {Y} where A is the coefficients of the polynomial
>	linSolver.solve(X, A, Y);
>	
>	//output
>	for (int j = 0; j <= degree; j++)
>		std::cout << A[j] << std::endl;
>	
>	//clean up
>	delete [] x;
>	delete [] y;
>}
>
>
>Any help is appreciated. Thank you.
>
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