Example 2: SparseMatrix Using the Matrix Market Format

The matrix market exchange format is an ASCII file format that represents sparse matrices in coordinate format. It consists of three sections: The header section is the first line in the file and contains general information about the matrix, e.g. data type and symmetry properties. This line is followed by the comments section which consists of zero or more lines of comments. The remainder of the file is the data section. The first line of the data section contains the row number, column number, and number of nonzeros of the matrix. The following lines contain the location and value of all nonzero entries of the matrix, usually one per line. A file in Matrix Market format is read and converted to a JMSL SparseMatrix in this example. Matrix information and the one norm of the matrix are printed. 
import com.imsl.math.*;
import java.io.*;

public class  SparseMatrixEx2 {
    
    public static class MTXReader {
        private String typecode;
        private SparseMatrix matrix;
        
        public void read(String filename) throws java.io.IOException {
            InputStream s = SparseMatrixEx2.class.getResourceAsStream(filename);
            BufferedReader br = new BufferedReader(new InputStreamReader(s));
            
            // read type code initial line
            String line = br.readLine();
            typecode = line;
            
            // read comment lines if any
            boolean comment = true;
            while (comment) {
                line = br.readLine();
                comment = line.startsWith("%");
            }
            
            // line now contains the size information which needs to be parsed
            String[] str = line.split("( )+");
            int nRows = (Integer.valueOf(str[0].trim())).intValue();
            int nColumns = (Integer.valueOf(str[1].trim())).intValue();
            int nNonZeros = (Integer.valueOf(str[2].trim())).intValue();
            
            // now we're into the data section
            matrix = new SparseMatrix(nRows, nColumns);
            while (true) {
                line = br.readLine();
                if (line == null)  break;
                str = line.split("( )+");
                int i = (Integer.valueOf(str[0].trim())).intValue();
                int j = (Integer.valueOf(str[1].trim())).intValue();
                double x = (Double.valueOf(str[2].trim())).doubleValue();
                matrix.set(i-1, j-1, x);
            }
            br.close();
        }
        
        public String getTypeCode() {
            return this.typecode;
        }        
    }
    
    public static void main(String args[]) throws Exception {
        MTXReader mr = new MTXReader();
        mr.read("bcsstk01.mtx");
        SparseMatrix A = mr.matrix;
        
        // Print the matrix type
        System.out.println("The matrix type is "+ mr.getTypeCode());
        
        // Print the matrix information and its one norm
        System.out.println("The number of rows is " + A.getNumberOfRows());
        int ncols = A.getNumberOfColumns();
        System.out.println("The number of columns is " +ncols);
        long nnz = A.getNumberOfNonZeros();
        System.out.println("The number of nonzero elements is " + nnz);
        System.out.println();
        System.out.println("The 1 norm of the matrix is "+ A.oneNorm());
    }
}

Output

The matrix type is %%MatrixMarket matrix coordinate real symmetric
The number of rows is 48
The number of columns is 48
The number of nonzero elements is 224

The 1 norm of the matrix is 3.00944444444744E9
Link to Java source.