Mathematica Asked by tom houston on March 6, 2021
comp1a = Flatten[Join[{{0 + 0 i}}, {comp1}]];
Flatten[comp1a[[1 ;; 6]]]
This creates a list of complex values -> comp1a
The first 6 terms in the list are:
{0, -2.04375 + 1.33694 I, -1.0492 + 3.3731 I, -4.95694 +
1.01694 I, 4.61625 – 4.52896 I, 6.66754 – 4.1488 I}
Then I try to pass the list to;
ExternalEvaluate["Python", "import numpy as np; timhist = np.fft.ifft(comp1a); timehist.tolist()"]
and the result is;
Failure
Message:"name ‘comp1a’ is not defined
Tag:PythonError
My question is how do I feed a list developed in Mathematica to a python function called externally
This will not work. Python does not know what mylist
is:
mylist = {1, 2, 3, 4};
ExternalEvaluate["Python", "sum(mylist)"]
You must get the value of mylist
into Python somehow. This could be done with string replacement:
ExternalEvaluate["Python", "sum(" <>
StringReplace[ToString[mylist], {"{" -> "[", "}" -> "]"}]
<> ")"]
... though as Jason .B noted in the comments, it's much simpler to write this as a TemplateExpression
:
ExternalEvaluate["Python", "sum(<* mylist *>)"]
For complex numbers, you'll need to rewrite them as a complex
type first before you can feed them to Python:
createcomplex[z_?NumericQ] :=
"complex(" <> ToString[Re[z]] <> "," <> ToString[Im[z]] <> ")"
createcomplex[-2.7 + 3.5 I]
(* result: "complex(-2.7,3.5)" *)
Or more simply, using templates:
toPyComplexStr[z_?NumericQ] :=
TemplateApply["complex(<* Re[z] *>, <* Im[z] *>)", z]
There is however, a better way in the documentation which doesn't depend on text substitution and it uses an external session:
session = StartExternalSession["Python"];
ExternalEvaluate[session, <|
"Command" -> "sum",
"Arguments" -> {NumericArray[{1 + I, 2.3 - I, 5.7 - 2.3 I, 7},
"ComplexReal32"]}
|>]
(* result: 16. - 2.3 I *)
Let's use it for your problem:
session = StartExternalSession["Python"];
result = Last@
ExternalEvaluate[
session, {"import numpy as np", <|"Command" -> "np.fft.ifft",
"Arguments" -> {NumericArray[{0, -2.04375 + 1.33694 I, -1.0492 +
3.3731 I, -4.95694 + 1.01694 I, 4.61625 - 4.52896 I,
6.66754 - 4.1488 I}, "ComplexReal32"]}|>}]
Normal[result]
(* result: {0.538983 - 0.491797 I, -1.01814 - 2.38259 I, -1.15996 + 0.0605042 I,
0.650033 + 0.10651 I, -1.85749 + 0.939762 I, 2.84658 + 1.76761 I} *)
... and notice that this result matches up with InverseFourier
if you use FourierParameters -> {1, -1}
:
InverseFourier[{0, -2.04375 + 1.33694 I, -1.0492 + 3.3731 I, -4.95694 + 1.01694 I, 4.61625 - 4.52896 I, 6.66754 - 4.1488 I},
FourierParameters -> {1, -1}]
(* result: {0.538983 - 0.491797 I, -1.01814 - 2.38259 I, -1.15996 + 0.0605042 I,
0.650033 + 0.10651 I, -1.85749 + 0.939762 I, 2.84658 + 1.76761 I} *)
Answered by flinty on March 6, 2021
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