Operation of vector elements

#1 Pubblicato: 08/03/2019 03:11:59

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Is it possible to assign specific values to specific elements and take the absolute value of other specific elements of a large vector with say 400 elements? I have tried for loops and if structure to no avail. I assume I just still don't understand the syntax in SMath.

#2 Pubblicato: 08/03/2019 03:48:51

Alvaro

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Hi. Something like this?

vector.sm (6,15 KiB) scaricato 1225 volta(e).

Best regards.
Alvaro.

#3 Pubblicato: 08/03/2019 04:34:04

RegCurry

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Thanks for your help.
What if I don’t know the positions that need changing ahead of time? In my vector of about 400 elements, some values are negative. I would like to change only those values to about 10^-10 or take their absolute value and leave all the other elements of the vector unchanged because I plan to plot the vector on a log-log plot.

This is quite easy to do in Mathcad, but it seems SMath doesn’t have the same capability. When I try to test on a value of an element using SMath’s if statement to see if that vector element needs changing I get syntax errors in SMath.

I was hoping to use something like this, but it doesn’t work.

k := [1...length(I)]

A[k := if I[k<= 0
10^-10
else
I[k

Where I is the vector of about 400 elements

Forgive the [ since the forum doesn’t allow subcripts or less than or equal. I am on my iPad now and the forum also does not allow uploading jpg from my photos.

#4 Pubblicato: 08/03/2019 04:42:19

RegCurry

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Here is a better image.

#5 Pubblicato: 08/03/2019 04:50:14

Alvaro

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This?

vector.sm (4,61 KiB) scaricato 1176 volta(e).

Best regards.
Alvaro.

#6 Pubblicato: 08/03/2019 04:54:10

RegCurry

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Thanks much. I thought I tried that in using a program line, but I guess I had some typo.

Thanks again!

#7 Pubblicato: 08/03/2019 04:57:58

RegCurry

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I tried to click on thank for you, but I got an error. Perhaps the forum doesn’t like iPads.

Again I really appreciate your help.

#8 Pubblicato: 08/03/2019 04:58:28

Alvaro

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Hi. The method in your picture, using range vectors, fails because 'if' have an special evaluation method, For instance, the true or false parts are evaluated only if the condition results in true or false, respectively.

This method is a workaround, but isn't very efficient.

vector.sm (7,5 KiB) scaricato 1176 volta(e).

Best regards.
Alvaro.

1 utenti hanno apprezzato questo post

frapuano 08/03/2019 05:05:00

#9 Pubblicato: 08/03/2019 05:50:19

RegCurry

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Interesting; thanks for that also.

#10 Pubblicato: 08/03/2019 10:15:09

Jean Giraud

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Wrote
Is it possible to assign specific values to specific elements

The attached is not exactly what you are looking for,
suggestive of Bolean Find-Replace in matrix.

Your 400 long vector is not easy to inspect, you can Pack in matrix,
probably Find-Replace in that more visible Packed matrix, then
Unwrap the processed matrix back in vector.
IMHO, it does not make much sense to |absolute| a vector.
Does it mean the vector-creator is under-designed ?
Matrices-Vectors ... what you do in Mathcad, Smath does.
Easy to select-collect position of elements in vector,
then replace those selected elements by new values.
You seem to have several demands to the "Cat in the hat Fairy",
Maybe she has all and +++

Cheers ... Jean

Utilities Matrix Find_Replace.sm (21,22 KiB) scaricato 1203 volta(e).

#11 Pubblicato: 08/03/2019 11:18:10

Jean Giraud

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Wrote
Is it possible to assign specific values to specific elements

... more matrix utilities

Utilities Matrix Treasury_1.sm (394,93 KiB) scaricato 1249 volta(e).

#12 Pubblicato: 08/03/2019 12:10:27

Martin Kraska

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vector(1).sm (3,9 KiB) scaricato 1179 volta(e).

Technische Mechanik mit SMath Studio: https://link.springer.com/book/10.1007/978-3-658-50592-9

3 utenti hanno apprezzato questo post

sergio 08/03/2019 12:47:00, NDTM Amarasekera 08/03/2019 13:12:00, frapuano 08/03/2019 18:02:00

#13 Pubblicato: 08/03/2019 14:22:13

Jean Giraud

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... more stuff,
Easy to replace part of a vector or of a specified matrix-col
by a user vector at specified position.

Utilities Matrix Replace_in_Vector.sm (20,85 KiB) scaricato 1252 volta(e).

#14 Pubblicato: 09/03/2019 02:19:10

Jean Giraud

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Wrote
In my vector of about 400 elements, some values are negative.I would like to change only those values to about 10^-10 or take their absolute value and leave all the other elements of the vector unchanged because I plan to plot the vector on a log-log plot.

Reg: that's what we need the 400 long vector.
Supplementary instructions/abstract guidance too.

Forum SMath

Operation of vector elements - assign values to vector elements with for loop? - Messaggi