[Haskell-beginners] Automatic Differentiation

[Jonas Béal]

Hello,

I have some questions about the Automatic Differentiation package in
Haskell (https://hackage.haskell.org/package/ad-4.3.2.1/docs/Numeric-AD.html
)
I need to compute the jacobian with that method and I have a type problem,
here a simplified example in order to focus on the error:

According to documentation I need to write "*jacobian function values*". So
I built the input *function. *Please notice this is important for me that
my function may depend on an external parameter (named factor here)
testFunctionForJacobian :: Fractional a => a -> [a] -> [a]
testFunctionForJacobian factor inputs = [(sum inputs) * factor]

Then, using *jacobian* function of Numeric.AD in terminal, as a test, it
works perfectly
>jacobian (testFunctionForJacobian 2) [1,2]
< [[2.0,2.0]]

No apparent type problem here
> :t (testFunctionForJacobian 2)
(testFunctionForJacobian 2) :: Fractional a => [a] -> [a]

But, I would like to insert that in a bigger function computing the jacobian
testJacobian :: Fractional a => a -> [a] -> [[a]]
testJacobian factor inputs = jacobian (testFunctionForJacobian factor)
inputs

This time it generates an error message about *factor*
Couldn't match expected type ‘Numeric.AD.Internal.Reverse.Reverse
<http://numeric.ad.internal.reverse.reverse/> s a’ with actual type ‘a’
‘a’ is a rigid type variable bound by the type signature for
testJacobian :: Fractional a => a -> [a] -> [[a]] s a’

All in all, my type seems implicitly correct in the terminal example but I
did not manage to write it explicitly in my function.

Here the *jacobian* function signature to help you answer me:






-- 
Jonas Béal

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