BrentSearch find root, min and max from string input

Question

I'm building scientific calculator for school project and have to implement quadratic equatation for functions with x,y in [a,b] So I'm using Accord.Net and Have managed to use it but I want to automate the process..

I have this code:

Func<double, double> function = x => x * x * x + 2 * x * x - 10 * x;
        Accord.Math.Optimization.BrentSearch search = new Accord.Math.Optimization.BrentSearch(function, -4, 3);
        double max = search.Maximize();
        double min = search.Minimize();
        double root = search.FindRoot();

But I need to do something like this:

string temp = Input.Text.ToString();
        Func<double, double> function = x => temp; //doesn't want string, and BrentSearch wants func<double,double>
        Accord.Math.Optimization.BrentSearch search = new Accord.Math.Optimization.BrentSearch(function, -4, 3);
        double max = search.Maximize();
        double min = search.Minimize();
        double root = search.FindRoot();

The thing is that Func don't accept string and BrentSearch wants func

Also the input comes from textbox and user manualy type the function..

Thank you!!!!!!!

Answer 1

This is not a simple task. You're actually trying to convert user input into C# code - which is essentially the same thing the C# compiler does!

If you want to give it a shot, it is possible to leverage the C# compiler to do the parsing for you.

using System;
using System.CodeDom.Compiler;
using System.Collections.Generic;
using System.Text;
using Microsoft.CSharp;

private static Func<double, double> CompileFunction(string expression)
{
    StringBuilder sourceBuilder = new StringBuilder();
    sourceBuilder.AppendLine("using System;");
    sourceBuilder.AppendLine("using System.Linq.Expressions;");
    sourceBuilder.AppendLine("class ExpressionGenerator{");
    sourceBuilder.AppendLine("public static Func<double, double> Generate(){");
    sourceBuilder.AppendLine("return x => " + expression + ";");
    sourceBuilder.AppendLine("}}");


    Dictionary<string, string> providerOptions = new Dictionary<string, string>();
    providerOptions.Add("CompilerVersion", "v3.5");
    CSharpCodeProvider provider = new CSharpCodeProvider(providerOptions);
    CompilerParameters parameters = new CompilerParameters(new[] { "System.Core.dll" });
    CompilerResults results = provider.CompileAssemblyFromSource(parameters, sourceBuilder.ToString());
    return (Func<double, double>)results.CompiledAssembly.GetType("ExpressionGenerator").GetMethod("Generate").Invoke(null, null);
}

You can call this function like this:

string input = "x * x";  // Or however you get the input
Func<double, double> myFunction = CompileFunction(input);

You'll still need to handle things like syntax errors in the provided strings, etc.