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## How to correct the Pell(n) function ? (for n = 181)

Hello Everyone,

How to correct the Pell(n) function ? ( for n = 181)

Thanks in advance for your time and help.

Regards.

1 ACCEPTED SOLUTION

Accepted Solutions

## Re: How to correct the Pell(n) function ? (for n = 181)

For some N (like 2,5,10) m is just 1 (second element of C is already greater than the root of N) and so your calculation of the rearranged vector c fails. Either include another if-statement to cope with that case (then c<--C) or do it completely different like in the attached.

14 REPLIES 14

## Re: How to correct the Pell(n) function ? (for n = 181)

Looking at Numerical Recipes, I think you need to add a correction factor in for when w[0,1 is zero.

Stuart

## Re: How to correct the Pell(n) function ? (for n = 181)

I greatly appreciate your help, Stuart.

With :

Best Regards.

## Re: How to correct the Pell(n) function ? (for n = 181)

Unfortunately, I'm Mathcadless for a week or so, but you can define your function as follows.

Rename my function to PellA.

Define

Pell(n):=p <-PellA(n, infinity)

stack (p[1, p[2)

thenPell(P181).

Stuart

## Re: How to correct the Pell(n) function ? (for n = 181)

Hello Everyone again,

Now I need help with correcting the Pell_Test(N) function, the above. ("This array index is invalid for this array")

Thanks in advance for your time and help.

Best Regards.

## Re: How to correct the Pell(n) function ? (for n = 181)

For some N (like 2,5,10) m is just 1 (second element of C is already greater than the root of N) and so your calculation of the rearranged vector c fails. Either include another if-statement to cope with that case (then c<--C) or do it completely different like in the attached.

## Re: How to correct the Pell(n) function ? (for n = 181)

I greatly appreciate your help. The answer is very neat . Many, many thanks, Werner.

By the way, I need help with how to type "the thin equal sign" (the green circle) in Mathcad 14.

Best Regards.

Message was edited by: Loi Le

## Re: How to correct the Pell(n) function ? (for n = 181)

 By the way, I need help with how to type "the thin equal sign" (the green circle) in Mathcad 14.

Same way as the * and the +. If you create a math region and you type Ctrl-Shift-K (cursor gets red as in a text region) you can use literally any character in a variable name. Pressing Ctrl-Shift-K again brings you back to normal mode. That way you can use characters in variable names which normally would be taken as operators. The sam way you can also insert some spaces instead of using the underline character as you had done.

## Re: How to correct the Pell(n) function ? (for n = 181)

I got it. . Many, many, many thanks, Werner. .

Best Regards.

## Re: How to correct the Pell(n) function ? (for n = 181)

I guess the Pell_Test(N) function need to adjust a little bit :

after adjusting a little bit :

And while I am learning about match( ) , submatrix( ) function, I adjust the function a little bit :

Thanks again.

Best Regards.

Message was edited by: Loi Le

Or :

Regards.

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