Sigma character - TYPE returns 3 (function)

[deSitter]

Where is this function defined? I want to use sigma for a list. Thanks in advance.

-drl

[Wes Loewer]

(12-17-2023 03:47 AM)deSitter Wrote:  Where is this function defined? I want to use sigma for a list. Thanks in advance.

Press the toolbox key, then in the Math menu select List then scroll down till you see Σ List. You can use it with a list variable, such as ΣLIST(L1), or with a list directly, such as ΣLIST({1,2,3}).

Is this what you had in mind?

[deSitter]

(12-17-2023 04:19 AM)Wes Loewer Wrote:  

(12-17-2023 03:47 AM)deSitter Wrote:  Where is this function defined? I want to use sigma for a list. Thanks in advance.

Press the toolbox key, then in the Math menu select List then scroll down till you see Σ List. You can use it with a list variable, such as ΣLIST(L1), or with a list directly, such as ΣLIST({1,2,3}).

Is this what you had in mind?

Thanks but no - lowercase sigma. I am setting up my calculator for doing quantum field theory. I need lowercase sigma for a list containing the 4 Pauli sigma matrices (one of them is 2d identity). This works for gamma for the Dirac gamma matrices because gamma is not defined anywhere - but somewhere, likely an app, sigma is defined as a function (type 2 not 3 that was a typo). It must be a globally defined function so I assume it is living in some useless app.

thanks

-drl

[Didier Lachieze]

Lower case sigma is defined as a function but you can add an indice such as 0, 1, 2 or a letter to create a variable name: σ0, σ₀ ….

[deSitter]

(12-17-2023 10:41 AM)Didier Lachieze Wrote:  Lower case sigma is defined as a function but you can add an indice such as 0, 1, 2 or a letter to create a variable name: σ0, σ₀ ….

Yes but I'm curious what the function is! I looked through every parameter of every standard app and no can find.

It's a shame we have no access to internals so these useless apps can be deleted.

-drl

[Didier Lachieze]

(12-17-2023 01:58 PM)deSitter Wrote:  Yes but I'm curious what the function is! I looked through every parameter of every standard app and no can find.

It’s the Sigma function. Place σ in the command line and press Help:

Quote:Σ -Summation

Syntax:
Σ(expr, var, ivalue, fvalue)

Finds the sum of expr with respect to var as var goes from ivalue to fvalue in steps of 1.


Examples:
Σ(X²,X,1,5) → 55
Σ({'X^2','Y-3'},{'X','Y'},{1,3},{5,10}) → {55,28}

[deSitter]

(12-17-2023 05:38 PM)Didier Lachieze Wrote:  

(12-17-2023 01:58 PM)deSitter Wrote:  Yes but I'm curious what the function is! I looked through every parameter of every standard app and no can find.

It’s the Sigma function. Place σ in the command line and press Help:

Quote:Σ -Summation

Syntax:
Σ(expr, var, ivalue, fvalue)

Finds the sum of expr with respect to var as var goes from ivalue to fvalue in steps of 1.


Examples:
Σ(X²,X,1,5) → 55
Σ({'X^2','Y-3'},{'X','Y'},{1,3},{5,10}) → {55,28}

NOT the summation function! I may have been born yesterday but I converged all night Lower case sigma. I just want to use the Greek character. There is a collision somewhere, I assumed int statistics apps, but can't find it in there.

-drl

[rawi]

This is really strange. If I put lower case sigma in the command line with or without brackets following and press enter I get "syntax error". It is not possible to store a number in this Greek letter.

[Didier Lachieze]

As indicated by the help it is the summation function, place σ(X²,X,1,5) in the command line, press ENTER and you’ll get 55.

[BruceH]

(12-18-2023 02:18 PM)rawi Wrote:  This is really strange. If I put lower case sigma in the command line with or without brackets following and press enter I get "syntax error". It is not possible to store a number in this Greek letter.

Think of it this way: you can't use 'sin' as a variable, e.g. sin:=3 because sin is the lowercase of SIN which is a function. Similarly σ is the lowercase of Σ which is a function.

[toml_12953]

(12-18-2023 01:59 PM)deSitter Wrote:  

(12-17-2023 05:38 PM)Didier Lachieze Wrote:  It’s the Sigma function. Place σ in the command line and press Help:

NOT the summation function! I may have been born yesterday but I converged all night Lower case sigma. I just want to use the Greek character. There is a collision somewhere, I assumed int statistics apps, but can't find it in there.

-drl

But it IS the summation function. Upper or lowercase sigma is used for summation. Try it and see.
It's case independent.

[deSitter]

(12-19-2023 04:16 AM)toml_12953 Wrote:  

(12-18-2023 01:59 PM)deSitter Wrote:  NOT the summation function! I may have been born yesterday but I converged all night Lower case sigma. I just want to use the Greek character. There is a collision somewhere, I assumed int statistics apps, but can't find it in there.

-drl

But it IS the summation function. Upper or lowercase sigma is used for summation. Try it and see.
It's case independent.

Yes, unfortunate. Time for a new operating system! In physics the sigma matrices have an almost religious iconic significance because of their connection with spin 1/2. Alas I must use tau now! Thanks everyone for clarifying.

-drl

[Wes Loewer]

(12-19-2023 09:05 AM)deSitter Wrote:  In physics the sigma matrices have an almost religious iconic significance because of their connection with spin 1/2. Alas I must use tau now! Thanks everyone for clarifying.

I can't help but wonder whether using σ for Σ was an accident or intentional. I have seen σ used for population standard deviation in statistics, surface density in physics, and the sum of the divisors in math, but I have I have never seen σ used for a Σ summation.

[deSitter]

(12-19-2023 11:57 AM)Wes Loewer Wrote:  

(12-19-2023 09:05 AM)deSitter Wrote:  In physics the sigma matrices have an almost religious iconic significance because of their connection with spin 1/2. Alas I must use tau now! Thanks everyone for clarifying.

I can't help but wonder whether using σ for Σ was an accident or intentional. I have seen σ used for population standard deviation in statistics, surface density in physics, and the sum of the divisors in math, but I have I have never seen σ used for a Σ summation.

Nor I. I would have been OK with it being co-opted by statistics. I'm miffed by this case insensitivity!

-drl

[Tim Wessman]

Guessing it is a side effect of the function mapping... I think from memory there is case insensitivity to avoid problems like Sin not mapping to SIN when using PC/Phone os versions, so later began using the more complete "tolower" type of function and it correctly mapped the SIGMA to sigma.

Although in this case probably wrong

[jte]

I created a ticket for this in the bug tracker I set up to help organize development … and this has now been modified, so that case insensitivity is not applied to Greek letters when looking for identifier matches against built-in functions. (So ‘Π’ and ‘σ’ will again be available for use as user variable names.)