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Guest Message by DevFuse

Next terms of two-dimensional sequences

6 replies to this topic

#1 bonanova

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Posted 25 April 2013 - 06:22 AM

Suppose I conjure a function f(x,y).

I give you a matrix of f values for x = {0 1 2 3 4 5 6} and y = {1 2 3 4 5 6}.
It looks like this:

x\y|  1  2  3  4  5  6
---+------------------
0  |  3  6  9 12 15 18
1  |  1  4  7 10 13 16
2  | -1  2  5  8 11 14
3  | -3  0  3  6  9 12
4  | -5 -2  1  4  7 10
5  | -7 -4 -1  2  5  8
6  | -9 -6 -3  0  3  6

From the first row you can see that f(0,y) = 3y
From the first column you can see that f(x,1) = 3-2x
From the second column it's clear that f(x,2) = 6-2x, and so forth.

At some point it's evident, and the other values so confirm, that f(x,y) = 3y-2x.

OK that's the idea. A 2-diminsional "what's the next term in this sequence" puzzle.
Only we don't ask the next term, we ask for the simplest function that generates the given terms.

See if this one is too easy (there are plenty of clues in the table):

Same range of values for x and y as above.

x\y|  1  2   3    4    5     6
---+--------------------------
0  |  1  1   1    1    1     1
1  |  0  1   2    3    4     5
2  | -1  0   1    0   -7   -28
3  | -2 -1   0  -17 -118  -513
4  | -3  0  17    0 -399 -2800
5  | -4  7 118  399    0 -7849
6  | -5 28 513 2800 7849     0

What is f(x,y)?

If you like this puzzle type, then let the solver make one, and we'll keep the thread going.

Aligning a table like this is easy: just use Courier font.

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Vidi vici veni.

#2 jamieg

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Posted 25 April 2013 - 02:56 PM

Very cool puzzle, I'd love to see more (some harder, but some at this level as well).

Spoiler for Solution

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#3 jamieg

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Posted 25 April 2013 - 03:01 PM

x\y    1   2   3   4   5   6

0    -2  -2  -2  -2  -2  -2

1    -1   0   1  -2  -1   0

2     0  -2   0  -2   0  -2

3     1   0  -1  -2   1   0

4    -2  -2  -2  -2  -2  -2

5    -1   0   1  -2  -1   0

6     0  -2   0  -2   0  -2

Edited by jamieg, 25 April 2013 - 03:04 PM.

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#4 googon97

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Posted 25 April 2013 - 11:52 PM

x\y    1   2   3   4   5   6

0      -2  -2  -2  -2  -2

1    -1   0   1  -2  -1   0

2     0  -2   0  -2   0  -2

3     1   0  -1  -2   1   0

4    -2  -2  -2  -2  -2  -2

5    -1   0   1  -2  -1   0

6     0  -2   0  -2   0  -2

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#5 googon97

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Posted 26 April 2013 - 12:01 AM

sorry apparently pressing space 6 times posts it 6 times.

1    2    3    4    5   6

0    0    0    0    0    0    0

1    2    6   12   20   30   42

2    6   16  30   48   70   96

3   12  30  54  84   120  162

4   20  48  84 128 180 240

5   30  70 120 180 250 330

6   42  96 162 240 330 432

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#6 bonanova

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Posted 26 April 2013 - 06:40 AM

Spoiler for Looks like

x\y|  1  2  3   4   5   6
---+---------------------
0  |  1  0 -3  -8 -15 -24
1  |  3  3  1  -3  -9 -17
2  |  7  8  7   4  -1  -8
3  | 13 15 15  13   9   3
4  | 21 24 25  24  21  16
5  | 31 35 37  37  35  31
6  | 43 48 51  52  51  48

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#7 jamieg

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Posted 26 April 2013 - 03:04 PM

Nicely done on mine, googon97. Bonanova, I've solved yours:

Spoiler for these are getting tougher

Next:

x\y|  1   2   3   4   5   6
---+---------------------
0  |  4  10  28  82 244 730
1  |  1   7  25  79 241 727
2  |  7  13  31  85 247 733
3  | -5   1  19  73 235 721
4  | 19  25  43  97 259 745
5  |-29 -23  -5  49 211 697
6  | 67  73  91 145 307 793

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