CODEWITHSUNDEEP
javamatrixsystemlinear-algebracolt
Konstantinos_S
Konstantinos_S

Reputation: 65

How to solve linear system of equations using colt library in java

I want to solve the linear equation matrix*X=D using Colt library. I tried :

DoubleMatrix2D matrix;
matrix = new DenseDoubleMatrix2D(4,4);
for (int row = 0; row < 4; row++) {
    for (int column = 0; column < 4; column++) {
        // We set and get a cell value:             
        matrix.set(row,column,row+column);          
    }
}
DoubleMatrix2D D;
D = new DenseDoubleMatrix2D(4,1);
D.set(0,0, 1.0);
D.set(1,0, -1.0);
D.set(2,0, 91.0);
D.set(3,0, -5.0);
DoubleMatrix2D X;
X = solve(matrix,D);

but I get an error
"The method solve(DoubleMatrix2D, DoubleMatrix2D) is undefined for the type Test" , where Test is the name of the class.

What have I done wrong? Any ideas?...

Upvotes: 0

Views: 2944

Answers (2)

Vladimir Kostyukov
Vladimir Kostyukov

Reputation: 2552

You also can use la4j (Linear Algebra for Java) for this:

  • For determined systems m == n which is actually, your case:

    // The coefficient matrix 'a'
Matrix a = new Basic2DMatrix(new double[][] {
  { 1.0, 2.0, 3.0 },
  { 4.0, 5.0, 6.0 },
  { 7.0, 8.0. 9.0 }
});

// A right hand side vector, which is simple dense vector
Vector b = new BasicVector(new double[] { 1.0, 2.0, 3.0 });

// We will use standard Forward-Back Substitution method,
// which is based on LU decomposition and can be used with square systems
LinearSystemSolver solver = 
   a.withSolver(LinearAlgebra.FORWARD_BACK_SUBSTITUTION);

Vector x = solver.solve(b, LinearAlgebra.DENSE_FACTORY);

  • For overdetermined systems m > n the LinearAlgebra.LEAST_SQUARES solver can be used.

All the examples are taken from official web-site: http://la4j.org

Upvotes: 1

qiGuar
qiGuar

Reputation: 1804

The reason why you are getting this error is because method solve() is non-static and can't be accessed from main().

This should solve your problem:

Algebra algebra = new Algebra();
DoubleMatrix2D X = algebra.solve(matrix, D);

Upvotes: 1

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