Example Fixed Sized Matrices

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Array access adds a significant amount of overhead to matrix operations. A fixed sized matrix gets around that issue by having each element in the matrix be a variable in the class. EJML provides support for fixed sized matrices and vectors up to 6x6, at which point it loses its advantage. The example below demonstrates how to use a fixed sized matrix and convert to other matrix types in EJML.

External Resources:

Example

/**
 * In some applications a small fixed sized matrix can speed things up a lot, e.g. 8 times faster.  One application
 * which uses small matrices is graphics and rigid body motion, which extensively uses 3x3 and 4x4 matrices.  This
 * example is to show some examples of how you can use a fixed sized matrix.
 *
 * @author Peter Abeles
 */
public class ExampleFixedSizedMatrix {
    public static void main( String[] args ) {
        // declare the matrix
        DMatrix3x3 a = new DMatrix3x3();
        DMatrix3x3 b = new DMatrix3x3();

        // Can assign values the usual way
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                a.set(i, j, i + j + 1);
            }
        }

        // Direct manipulation of each value is the fastest way to assign/read values
        a.a11 = 12;
        a.a23 = 64;

        // can print the usual way too
        a.print();

        // most of the standard operations are support
        CommonOps_DDF3.transpose(a, b);
        b.print();

        System.out.println("Determinant = " + CommonOps_DDF3.det(a));

        // matrix-vector operations are also supported
        // Constructors for vectors and matrices can be used to initialize its value
        DMatrix3 v = new DMatrix3(1, 2, 3);
        DMatrix3 result = new DMatrix3();

        CommonOps_DDF3.mult(a, v, result);

        // Conversion into DMatrixRMaj can also be done
        DMatrixRMaj dm = DConvertMatrixStruct.convert(a, null);

        dm.print();

        // This can be useful if you need do more advanced operations
        SimpleMatrix sv = SimpleMatrix.wrap(dm).svd().getV();

        // can then convert it back into a fixed matrix
        DMatrix3x3 fv = DConvertMatrixStruct.convert(sv.getDDRM(), (DMatrix3x3)null);

        System.out.println("Original simple matrix and converted fixed matrix");
        sv.print();
        fv.print();
    }
}