function testGetVariables()
{
$e = new Expression('2*x + y*sin(4*x)');
$v = $e->getVariables();
$this->assertEqual(sizeof($v), 2);
$this->assertEqual($v[0], 'x');
$this->assertEqual($v[1], 'y');
}
/**
* Check that an equation is correct with the variable values in this problem.
* All variables in the equation must be defined in this problem.
* @param $str :: An equation as a string.
* @return :: A string 'true' if the equation is correct and error message otherwise.
*/
function checkEquation($str)
{
$e = new Expression($str);
if ($e->fun != '=') {
return 'not equation';
}
$vars = $e->getVariables();
$undef = $this->findUndefinedVariables($vars);
if (sizeof($undef) > 0) {
return 'undefined: ' . implode(', ', $undef);
}
$lhs = $e->terms[0];
$rhs = $e->terms[1];
$fun = $rhs->op;
$lv = $lhs->eval_double($this->vars);
$rv = $rhs->eval_double($this->vars);
$res = 'oops';
if ($fun == '=') {
$res = $lv == $rv ? 'true' : 'false';
} else {
if ($fun == '>') {
$res = $lv > $rv ? 'true' : 'false';
} else {
if ($fun == '<') {
$res = $lv < $rv ? 'true' : 'false';
} else {
if ($fun == '>=') {
$res = $lv >= $rv ? 'true' : 'false';
} else {
if ($fun == '<=') {
$res = $lv <= $rv ? 'true' : 'false';
}
}
}
}
}
return $res;
}
