Exception in thread “main” java.lang.RuntimeException: Matrix is singular

Question

I\'m just trying to create an inverse matrix of a 3x3 matrix following JAMA documentation. But every time it\'s giving me the following error -

Exception i

Answer 1

The documentation for Jama is not very good.

In fact, if you look through the sourcecode, you will find that Matrix.inverse() ultimately calls LUDecomposition.solve(...) and the code says:

  270      /** Solve A*X = B
  271      @param  B   A Matrix with as many rows as A and any number of columns.
  272      @return     X so that L*U*X = B(piv,:)
  273      @exception  IllegalArgumentException Matrix row dimensions must agree.
  274      @exception  RuntimeException  Matrix is singular.
  275      */
  277      public Matrix solve (Matrix B) {
  278         if (B.getRowDimension() != m) {
  279            throw new IllegalArgumentException("Matrix row dimensions must agree.");
  280         }
  281         if (!this.isNonsingular()) {
  282            throw new RuntimeException("Matrix is singular.");
  283         }

As Wikipedia says:

"In linear algebra an n-by-n (square) matrix A is called invertible or nonsingular or nondegenerate, if there exists an n-by-n matrix B such that AB = BA = I_n where I_n denotes the n-by-n identity matrix and the multiplication used is ordinary matrix multiplication."

In short, singular means not invertible.

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If you are unhappy with JAMA, take a look at the Apache Commons Maths libraries, in particular the Linear Algebra module.