// Global variables.
var hiLiteColor = '#ff3';
var normalColor = 'white';
var domCompliant = (document.getElementById);

function initFocus() {
	document.forms[0].elements[0].focus();
	}

function enter(thisId) {
	if (domCompliant) {
		nodeObj = document.getElementById(thisId);
		nodeObj.style.backgroundColor = hiLiteColor;
		}
	}

function exit(thisId) {
	if (domCompliant) {
		nodeObj = document.getElementById(thisId);
		nodeObj.style.backgroundColor = normalColor;
		}
	}

function clearSolutions(matrix, size) {
	offSet = size * size + size + 2;
	for (i = 0; i < size; i++) matrix[i+offSet].value = '';
	}

function validMatrix(matrix, size) {
	limit = size * size + size;
	valid = true;
	i = 0;
	while (i < limit && valid) {
		elementName = matrix[i].name;
		valid = !isNaN(matrix[i].value);
		i++;
		}
	if (!valid) {
		row = elementName.substring(1);
		col = elementName.substring(0,1);
		if (col == 's') variable = '"equal to" part'
		else variable = col.toUpperCase() + ' coefficient';
		alert('Oops! Must have a number in the ' + variable + ' of row ' + row + '.');
		matrix[element].focus();
		}
	return valid;
	}

function gcf(a, b) {
	if (a < b) t = a, a = b, b = t;
	remainder = a % b;
	while (remainder != 0 ) {
		a = b;
		b = remainder;
		remainder = a % b;
		}
	return b;
	}

function formatFraction(sign, n, d) {
	maxDigits = document.forms[1].limit.value;
	if (isNaN(maxDigits)) maxDigits = 2;
	maxDigits = (Math.floor(maxDigits));
	if (maxDigits < 0) maxDigits = -maxDigits;
	document.forms[1].limit.value = maxDigits;
	maxSize = Math.pow(10,maxDigits);
	if ((n < maxSize) && (d < maxSize)) value = (sign * n) + '/' + d
	else value = sign * n / d;
	return value;
	}

function reduce(n, d) {
	if (d == 0) return 'No Solution';
	if ((n / d) == Math.floor(n / d)) return n / d;
	else {
		sign = (n * d) / Math.abs(n * d);
		n = Math.abs(n);
		d = Math.abs(d);
		cd = gcf(n,d);
		value = formatFraction(sign, n/cd, d/cd);
		return value;
		}
	}