Use Inactive for Debugging a Program 

By activating parts of a program in stages, Inactive can assist the debugging process.

The following program contains an error.

In[1]:=

X a = 5.321122356674; b = -4.61014535141467; c = 0.214828315564808; d = 10.34234234234; min = -100; max = 100; kernel[x_, 1] := Exp[-(b - x)^2/c^2] kernel[x_, 2] := Max[Abs[b/c] - Abs[(b - x)/c], 0] firstInt[f_, x_, i_] := NIntegrate[d*kernel[x/a]*f, {x, min, max}] myInt[f_, x_, i_] := NIntegrate[f *firstInt[f, x, i], {x, min, max}]

Multiple messages are produced, and the integral returns unevaluated.

In[2]:=

X myInt[x^2 + 3 x + 7, x, 1]

Out[2]=

Create an inactive version of the program.

In[3]:=

X debugInt[f_, x_, i_] := Inactivate[NIntegrate[f *firstInt[f, x, i], {x, min, max}]]

In[4]:=

X debugInt[7 + 3 x + x^2, x, 1]

Out[4]=

Everything looks fine, so try activating the function .

In[5]:=

X Activate[debugInt[7 + 3 x + x^2, x, 1], firstInt]

Out[5]=

A message is produced, and the inner NIntegrate shows failed to evaluate—it is missing its second argument. Correct the definition.

In[6]:=

X firstInt[f_, x_, i_] := NIntegrate[kernel[x/a, i]*f, {x, min, max}]

Now evaluation proceeds correctly.

In[7]:=

X myInt[x^2 + 3 x + 7, x, 1]

Out[7]=

In[8]:=

X myInt[x^2 + 3 x + 7, x, 2]

Out[8]=