[racket] Advice on using math/array and math/matrix to rewrite MATLAB code

Thanks Jens and Alexander

That all helps. What I'm drawing from your responses:

* Write Racket code work; then add types until it checks.
* exact-ceiling is a thing.
* Get domains right (either with types or check & error).
* Try working mainly with matrices for this problem initially.
* Write functions in terms of Real's / Nonnegative-Real's, and use Flonum
data for performance.

In terms of developing a little proficiency I'll study those tests and work
through one or two Octave (GNU's Matlab alternative) tutorials with TR.


Thanks!

Dan


On Sun, May 4, 2014 at 6:10 AM, Alexander D. Knauth <alexander at knauth.org>wrote:

> This type-checks:
> #lang typed/racket
>
> (: log2 (Nonnegative-Real -> Real))
> (define (log2 x)
>   (/ (log x) (log 2)))
> Why don’t you just use this?
>
> On May 3, 2014, at 10:09 AM, Jens Axel Søgaard <jensaxel at soegaard.net>
> wrote:
>
> 2014-05-03 8:43 GMT+02:00 Daniel Prager <daniel.a.prager at gmail.com>:
>
> I'm having a go at converting a pitch detection algorithm from MATLAB to
> Typed Racket, and which I'll Open Source if I can get it working, and am
> after a few pointers, since I'm new to TR and am finding it slow going.
>
> Examples of the kind of code I'm writing in my fledlging attempts:
>
> #lang typed/racket
>
> (define: (log2 [x : Real]) : Real
>  (define result (/ (log x) (log 2)))
>  (if (real? result)
>      result
>      0.0))
>
>
> My strategy is write the write the function in normal Racket first:
>
>  (define (log2 x)
>      (/ (log x) (log 2)))
>
> Then to add the type:
>
>  (: log2 : Real -> Real)
>  (define (log2 x)
>      (/ (log x) (log 2)))
>
> In this case I get a type error, the result is not a Real but a Number.
> If x is negative, then (log x) is a complex number. I therefore need
> to insert a an explicit check that x is positive:
>
> (: log2 : Real -> Real)
> (define (log2 x)
>    (cond [(positive? x) (/ (log x) (log 2))]
>              [else             (error 'log2 "positive number expected")]))
>
> This version type checks.
>
> (define: (build-step-vector [min : Real] [step : Real] [max : Real]) :
>  (Vectorof Real)
>  (for/vector: : (Vectorof Real)
>      #:length (ceiling (inexact->exact (/ (- max min) step)))
>      ([i (in-naturals)])
>    (+ min (* i step))))
>
>
> Here I tried this version:
>
> (: step-vector : Real Real Real -> (Vectorof Real))
> (define (step-vector min max step)
>  (for/vector #:length (exact-ceiling (/ (- max min) step))
>    ([x (in-range min max step)])
>    x))
>
> This gave an error, since TR could only infer that the result was a
> (Vectorof Any).
> Then I changed it to:
>
> (: step-vector : Real Real Real -> (Vectorof Real))
> (define (step-vector min max step)
>  (for/vector: : (Vectorof Real) #:length (exact-ceiling (/ (- max min)
> step))
>    ([x (in-range min max step)])
>    x))
>
> Beyond that:
>
> Can anyone point me to examples of any code before/after converted from
> MATLAB (or Octave) to TR?
>
>
> I haven't any experience with either (except reading parts of the
> documentation).
> Do you have any particular examples in mind?
>
> What's a good scalar type to work with for floating point to start with?
>
>
> Flonum ?
>
> Which non-scalar type(s) should I favor: vectors, arrays or matrices?
>
>
> Matrices are just two-dimensional arrays. Therefore if there is a matrix
> operation missing, mostly likely you can find it in the array section
> of the documentation.
>
> If you stick with matrices, you can view vectors as nx1 matrices.
> This allows you to use the matrix operations on vectors.
>
> Depending on the operations you need, I'd try out matrices.
>
> Any general tips to develop facility for this kind of stuff? I feel like I
> need to go "back to basics", but there seems to be a dearth of examples and
> tutorials. on math/... beyond the reference materials.
>
>
> True.
>
> /Jens Axel
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users
>
>
>


-- 
*Daniel Prager*
Agile/Lean Coaching, Software Development and Leadership
Startup: www.youpatch.com
Twitter: @agilejitsu <https://twitter.com/agilejitsu>
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