# Difference between revisions of "Example Fixed Sized Matrices"

From Efficient Java Matrix Library

(2 intermediate revisions by the same user not shown) | |||

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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. | 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: | |

− | * [https://github.com/lessthanoptimal/ejml/blob/v0. | + | * [https://github.com/lessthanoptimal/ejml/blob/v0.31/examples/src/org/ejml/example/ExampleFixedSizedMatrix.java ExampleFixedSizedMatrix] |

+ | * <disqus>Discuss this example</disqus> | ||

== Example == | == Example == | ||

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public static void main( String args[] ) { | public static void main( String args[] ) { | ||

// declare the matrix | // declare the matrix | ||

− | + | DMatrix3x3 a = new DMatrix3x3(); | |

− | + | DMatrix3x3 b = new DMatrix3x3(); | |

// Can assign values the usual way | // Can assign values the usual way | ||

Line 36: | Line 37: | ||

// most of the standard operations are support | // most of the standard operations are support | ||

− | + | CommonOps_DDF3.transpose(a,b); | |

b.print(); | b.print(); | ||

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

// matrix-vector operations are also supported | // matrix-vector operations are also supported | ||

// Constructors for vectors and matrices can be used to initialize its value | // 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 | + | // Conversion into DMatrixRMaj can also be done |

− | + | DMatrixRMaj dm = DConvertMatrixStruct.convert(a,null); | |

dm.print(); | dm.print(); | ||

Line 57: | Line 58: | ||

// can then convert it back into a fixed matrix | // 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"); | System.out.println("Original simple matrix and converted fixed matrix"); |

## Latest revision as of 20:57, 4 November 2020

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();
}
}
```