public SparseVector plus(SparseVector b) {
		SparseVector a = this;
		if (a.N != b.N) throw new IllegalArgumentException("Vector lengths disagree : " + a.N + " != " + b.N);
		SparseVector c = new SparseVector(N);
		for (int i : a.symbolTable) c.put(i, a.get(i));                // c = a
		for (int i : b.symbolTable) c.put(i, b.get(i) + c.get(i));     // c = c + b
		return c;
	}
public SparseVector plus ( SparseVector b ) { SparseVector a = this ; if ( a . N != b . N ) throw new IllegalArgumentException ( "Vector lengths disagree : " + a . N + " != " + b . N ) ; SparseVector c = new SparseVector ( N ) ; for ( int i : a . symbolTable ) c . put ( i , a . get ( i ) ) ; for ( int i : b . symbolTable ) c . put ( i , b . get ( i ) + c . get ( i ) ) ; return c ; }
Calcualtes return a + b

@param b
@return