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Chapter 10 Solutions - Definition / Implementation mismatch for the logistic #49

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EricRobertCampbell opened this issue Oct 6, 2021 · 1 comment · May be fixed by #50
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Chapter 10 Solutions - Definition / Implementation mismatch for the logistic #49

EricRobertCampbell opened this issue Oct 6, 2021 · 1 comment · May be fixed by #50

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@EricRobertCampbell
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In the final exercise for Chapter 10, there is a slight mismatch between the definition of the 3-parameter logistic function and its implementation. In the definition, we see that the parameter a is multiplying the other term in the exponent of the exponential.

original

However, in the implementation in the next cell, we see that the variable a is dividing the rest of the terms (in the assignment to x).

original code

The Wikipedia link also uses the convention of having the parameter a multiply the terms. I believe that the easiest solution would be to change the value of a to 1/100 and change it to multiplication in the definition of x.
EricRobertCampbell added a commit to EricRobertCampbell/ThinkBayes2 that referenced this issue Oct 6, 2021
@EricRobertCampbell
Changed logistic model code to match description
1ff8ea7 
- In the final exercise, in the exponent of the exponential, the
  parameter `a` is multiplying the other term
- However, in the accompanying code, the parameter `a` is dividing it
- The accompanying Wikipedia link about Item Response Theory also uses
  the convention of multiplying in the factor `a`
- Easy fix: in the code switch `a` from `a = 100` to `a = 1 / 100`, and
  switch it it multiplication in the assignment to `x`
- Closes AllenDowney#49
@EricRobertCampbell EricRobertCampbell mentioned this issue Oct 6, 2021
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@AllenDowney
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Got it. Will fix. Thanks!

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Changed logistic model code to match description EricRobertCampbell/ThinkBayes2
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@AllenDowney @EricRobertCampbell