Understanding this Set error

Question

Given the toy vector:

elettrone={{1.5, 1.5, 0.064, 1.4289, -2.0901, 790.138},{1.5, 1.5, 0.064, 1.4289, -2.0901, 790.138},{1.5, 1.5, 0.064, 1.4289, -2.0901, 790.138}}

I try to change the first three elements as follows:

elettrone[[All, 1]][[1]] -= 
  dx*Sin[elettrone[[All, 4]][[1]]]*Cos[elettrone[[All, 5]][[1]]];
elettrone[[All, 2]][[1]] -= 
  dx*Sin[elettrone[[All, 4]][[1]]]*Sin[elettrone[[All, 5]][[1]]];
elettrone[[All, 3]][[1]] -= dx*Cos[elettrone[[All, 4]][[1]]];

with dx=0.0001. I get the error:

Set::partd: Part specification elettrone[[All,1,n]] is longer than depth of object.
<p>Set::partd: Part specification elettrone[[All,2,n]]
is longer than depth of object. </p>

<p>Set::partd: Part specification
elettrone[[All,3,n]] is longer than depth of object.</p>

How can this error appear I am not writing elettrone[[All,1,n]]!

I am using version 11.3 for windows

Not sure the exact source but it is probably related to the fact that you can't do a[[All, 1]][[2]] = ... you need to do a[[2, 1]] = .... See: Part not behaving the way I expect it to — Kuba, Sep 24 '18 at 11:14
If all else fails, you could consider using ReplacePart[]... — J. M.'s missing motivation, Sep 24 '18 at 11:21
After some inspection, we can clearly see that the toy code is only concerned with the very first sublist of elettrone. — LLlAMnYP, Sep 24 '18 at 11:59
By the way, I do not get n in version 10.2, I get 1, 2, and 3. — LLlAMnYP, Sep 24 '18 at 12:13

score 1 · Answer 1 · answered Sep 24 '18 at 12:10

The same thing that your code seems to want to do can be done by the following:

With[{dx = 0.0001}, 
 MapAt[
   {#1 - dx Sin[#4] Cos[#5], #2 - dx Sin[#4] Sin[#5], #3 - dx Cos[#4], #4, #5} & @@ # &,
   elettrone, {1}
 ]
]

or, to extend the same pattern to every sublist

{#1 - dx Sin[#4] Cos[#5], #2 - dx Sin[#4] Sin[#5], #3 - dx Cos[#4], #4, #5} & @@@ elettrone

Understanding this Set error

1 Answers1