removeLastOperatorChar();
//printing graph structures
if (!graphPrint.isEmpty()) {
if (sb.length() != 0)
sb.append(operatorChar);
OutputFormat printMatrixIndices = format.printMatrixIndices();
for (int i = 0; i < data.length; ++i)
if (graphPrint.get(i)) {
sb.append(data[i].toString(printMatrixIndices, Product.class));
sb.append(operatorChar);
}