Can't solve the mathematical expression using DDMathParser

Question

I am using DDMathParser to parse the string expressions. I am working on one expression which is "(2+x)6+2x+2y=5y+2x", I am trying to parse it and evaluate it using DDMathParser. It can be considered as first degree function that I need to solve using Objective C.

Guys any ideas?

Help would be highly appreciated.

DDExpression * e = [DDExpression expressionFromString:expression error:error];
NSNumber *num = [e evaluateWithSubstitutions:substitutions evaluator:nil error:error];

Answer 1

I don't know much about DDMathParser (OK, I don't know anything about it), but taking a look at the documentation gives some clues about what is going wrong with your code.

Based on the documentation, I could find not example of where DDMathParser could handle symbolic expressions. All of the examples on the Usage page show numeric expressions.

For symbolic math, see Symbolic Math Library in C/C++/Obj-C .

In addition, it looks like you are trying to solve for two variables with a single equation, which is certainly not going to result in a numeric solution.

However, if you are just trying to substitute values in for x and y, you should use the $ sign before them as the documentation says:

If you don't know what the value of a particular term should be when the string is constructed, that's ok; simply use a variable:

     NSString *math = @"6 * $a";

So if you just want to substitute values in your expression, try using:

string expression = @"(2+$x)6+2*$x+2*$y";

Then fill in with values.

NSDictionary *s = @{@"x" : 42, @"y" : 43};

And evaluate.

DDMathEvaluator *eval = [DDMathEvaluator sharedMathEvaluator];
NSLog(@"%@", [eval evaluateString:expression withSubstitutions:s]);