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Mathematics Equation Solving Wolfram Language

How to solve numerically an equation when NSolve is not appropriate?

Marcel Pelletier

Marcel Pelletier, Education

Posted 9 years ago

Hi, This is my code: In[1]:= f[x_] := x^2 In[2]:= g[a_, b_] := NIntegrate[f[x], {x, a, b}] In[3]:= g[1, 2] Out[3]= 2.33333 In[4]:= NSolve[g[1, b] == 3, b] During evaluation of In[4]:= NIntegrate::nlim: x = b is not a valid limit of integration. >> I am unable to Numericaly Solve for the variable b. Marcel

Hi, This is my code:

    In[1]:= f[x_] := x^2
    In[2]:= g[a_, b_] := NIntegrate[f[x], {x, a, b}]
    In[3]:= g[1, 2]     
    Out[3]= 2.33333  
    In[4]:= NSolve[g[1, b] == 3, b]
    During evaluation of In[4]:= NIntegrate::nlim: x = b is not a valid limit of integration. >>

I am unable to Numericaly Solve for the variable b.

Marcel

POSTED BY: Marcel Pelletier

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Frank Kampas

Frank Kampas, Physicist at Large Consulting

Posted 9 years ago

FindRoot works with polynomials and related symbolic expressions. In[7]:= f[x_] = x^2; g[a_?NumberQ, b_?NumberQ] := NIntegrate[f[x], {x, a, b}] In[9]:= FindRoot[g[1, b] == 3, {b, 1}] Out[9]= {b -> 2.15443}

POSTED BY: Frank Kampas

Marcel Pelletier

Marcel Pelletier, Education

Posted 9 years ago

Hi, Thank you for your help! Marcel

POSTED BY: Marcel Pelletier

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