Wolfram Mathematica

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YungHummmma

02:50

I have a question that I don't know how to google effectively

How can I make a list of variables that aren't explicitly named?

for example, let's say some function is going to return N functions to me, and I want to fit a variable for each one to the sum of them, but I don't know in advance how many there will be

halirutan

@YungHummmma That doesn't make sense. If you don't need names, you don't need a variable in the first place.

YungHummmma

I'm probably explaining this really badly...

halirutan

Can you give a simple example?

YungHummmma

Let's say I get some list of functions of the form a*x^b, and for each one, a is specified, but b is left vague, as a fit parameter

halirutan

OK.

YungHummmma

02:54

and then I want to do FindMinimum[Total[listofaxb]], fitting for all the b's

but I want b to be different for each one, the fit parameters are the list of different b's

halirutan

@YungHummmma How do you create this list of {a*x^b, ...}?

YungHummmma

I dunno, a table or something

halirutan

Then the solution is simple

YungHummmma

like Table[i*x^b,{i,4}]

Hmm what do you have in mind?

halirutan

exp = Table[With[{b = Unique["b"]}, {b, i*x^b}], {i, 4}]
Transpose[%]

You use the table for both building your expression and collecting which symbol b you have created.

YungHummmma

02:58

Ahh... I've never seen Unique before... let me check that out!

ahhhh this seems perfect

Thank you!

halirutan

Then go ahead and try your FindMinimum code..

YungHummmma

Sure, gimme a min

YungHummmma

03:14

uuughhh

damn it

I don't get what's happening when FindMinimum finds values that are less accurate than the initial values I give it...

neeeever mind, I'm an idiot

I should figure out the order of operations one of these days...

or just be extra explicit with parentheses...

real purdy, thank you!

14 hours later…

Wolfram Blog

17:20

Wolfram Blog: Map Projections and the Center of the US

posted on July 14, 2017 by Brian Wood

In 1918, the National Geodetic Survey (or NGS, at that time the United States Coast and Geodetic Survey) used its compiled geodetic data to compute the geographic center of the contiguous United States as 39°50′N 98°35′W. Their methodology—balancing a cardboard cutout of the lower 48 states at a point—was rudimentary but surprisingly effective, coming within [...]

5 hours later…

halirutan

22:35

So we are 2 people in this room, not counting Tim Stone? On a Friday night..

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