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Geometric Betting Math Geometric Betting Math

08-05-2016 , 11:33 AM
From Math of Poker, Geometric Betting is described as betting a constant fraction of the pot over 3 streets so that you are all in on the river (again betting the same fraction of that pot). i.e. pot is $200, and you have a stack size of 2600 you need to constantly bet 100% of pot on each street to be all in on the river with the same fraction bet size.

I'm wondering how to approach this if i want to solve this with a function for all stack sizes and pot sizes. i.e. let S be the effective stack size, and P be pot size and then the function returns the percentage need to be bet on each street. But i haven't drank enough coffee to even get a grasp on how to start this.
Geometric Betting Math Quote
08-05-2016 , 03:38 PM
The solution is a cubic equation, which can be somewhat complicated to solve. If your stack size is k * pot then the equation is

4*f^3 + 6*f^2 + 3*f - k = 0,

where f is the constant bet fraction.

Rather than solve this mathematically (I don't know if this is an easy one), you can put this equation in Excel and let its Goal Seek function do the job or you can use an on-line solver such as at http://www.1728.org/cubic.htm

Example: At the flop, pot is 100 and your stack size is 500, so k = 5. GoalSeek gives f = 61.2%%. Doing the arithmetic, you bet 61 on the flop, 136 on the turn and the rest, 303 on the river.
Geometric Betting Math Quote
08-05-2016 , 09:51 PM
From (2*b + 1)3 = 2*s + 1 where s = Stack/Pot and solving for the betting fraction b you get:
b = ((2*s + 1)1/3 - 1)/2
Geometric Betting Math Quote
08-25-2016 , 07:07 PM
Quote:
Originally Posted by R Gibert
From (2*b + 1)3 = 2*s + 1 where s = Stack/Pot and solving for the betting fraction b you get:
b = ((2*s + 1)1/3 - 1)/2
This generalizes to any number (=n) of streets:
b = ((2*s + 1)1/n - 1)/2
Unfortunately, computing roots at the table is not so easy, but we should not let this stop us from trying. The following 2 approximations are within a few percent of being accurate at computing the betting fraction b. For 3 streets:
b = (s + 7)/20
with a useful range of about 3.2 ≤ s ≤ 15.4
Code:
   s     ≈      =     Δ
  3.1  50.5%  46.5% +4.0%
  3.2  51.0%  47.4% +3.6%
  3.3  51.5%  48.3% +3.2%
  3.4  52.0%  49.2% +2.8%
  3.5  52.5%  50.0% +2.5%
  3.6  53.0%  50.8% +2.2%
  3.7  53.5%  51.6% +1.9%
  3.8  54.0%  52.4% +1.6%
  3.9  54.5%  53.2% +1.3%
  4.0  55.0%  54.0% +1.0%
  4.1  55.5%  54.8% +0.7%
  4.2  56.0%  55.5% +0.5%
  4.3  56.5%  56.3% +0.2%
  4.4  57.0%  57.0% +0.0%
  4.5  57.5%  57.7% -0.2%
  4.6  58.0%  58.4% -0.4%
  4.7  58.5%  59.1% -0.6%
  4.8  59.0%  59.8% -0.8%
  4.9  59.5%  60.5% -1.0%
  5.0  60.0%  61.2% -1.2%
  5.1  60.5%  61.9% -1.4%
  5.2  61.0%  62.5% -1.5%
  5.3  61.5%  63.2% -1.7%
  5.4  62.0%  63.8% -1.8%
  5.5  62.5%  64.5% -2.0%
  5.6  63.0%  65.1% -2.1%
  5.7  63.5%  65.7% -2.2%
  5.8  64.0%  66.3% -2.3%
  5.9  64.5%  67.0% -2.5%
  6.0  65.0%  67.6% -2.6%
  6.1  65.5%  68.2% -2.7%
  6.2  66.0%  68.8% -2.8%
  6.3  66.5%  69.3% -2.8%
  6.4  67.0%  69.9% -2.9%
  6.5  67.5%  70.5% -3.0%
  6.6  68.0%  71.1% -3.1%
  6.7  68.5%  71.6% -3.1%
  6.8  69.0%  72.2% -3.2%
  6.9  69.5%  72.8% -3.3%
  7.0  70.0%  73.3% -3.3%
  7.1  70.5%  73.9% -3.4%
  7.2  71.0%  74.4% -3.4%
  7.3  71.5%  74.9% -3.4%
  7.4  72.0%  75.5% -3.5%
  7.5  72.5%  76.0% -3.5%
  7.6  73.0%  76.5% -3.5%
  7.7  73.5%  77.0% -3.5%
  7.8  74.0%  77.5% -3.5%
  7.9  74.5%  78.1% -3.6%
  8.0  75.0%  78.6% -3.6%
  8.1  75.5%  79.1% -3.6%
  8.2  76.0%  79.6% -3.6%
  8.3  76.5%  80.1% -3.6%
  8.4  77.0%  80.5% -3.5%
  8.5  77.5%  81.0% -3.5%
  8.6  78.0%  81.5% -3.5%
  8.7  78.5%  82.0% -3.5%
  8.8  79.0%  82.5% -3.5%
  8.9  79.5%  83.0% -3.5%
  9.0  80.0%  83.4% -3.4%
  9.1  80.5%  83.9% -3.4%
  9.2  81.0%  84.3% -3.3%
  9.3  81.5%  84.8% -3.3%
  9.4  82.0%  85.3% -3.3%
  9.5  82.5%  85.7% -3.2%
  9.6  83.0%  86.2% -3.2%
  9.7  83.5%  86.6% -3.1%
  9.8  84.0%  87.1% -3.1%
  9.9  84.5%  87.5% -3.0%
 10.0  85.0%  87.9% -2.9%
 10.1  85.5%  88.4% -2.9%
 10.2  86.0%  88.8% -2.8%
 10.3  86.5%  89.2% -2.7%
 10.4  87.0%  89.7% -2.7%
 10.5  87.5%  90.1% -2.6%
 10.6  88.0%  90.5% -2.5%
 10.7  88.5%  90.9% -2.4%
 10.8  89.0%  91.4% -2.4%
 10.9  89.5%  91.8% -2.3%
 11.0  90.0%  92.2% -2.2%
 11.1  90.5%  92.6% -2.1%
 11.2  91.0%  93.0% -2.0%
 11.3  91.5%  93.4% -1.9%
 11.4  92.0%  93.8% -1.8%
 11.5  92.5%  94.2% -1.7%
 11.6  93.0%  94.6% -1.6%
 11.7  93.5%  95.0% -1.5%
 11.8  94.0%  95.4% -1.4%
 11.9  94.5%  95.8% -1.3%
 12.0  95.0%  96.2% -1.2%
 12.1  95.5%  96.6% -1.1%
 12.2  96.0%  97.0% -1.0%
 12.3  96.5%  97.4% -0.9%
 12.4  97.0%  97.7% -0.7%
 12.5  97.5%  98.1% -0.6%
 12.6  98.0%  98.5% -0.5%
 12.7  98.5%  98.9% -0.4%
 12.8  99.0%  99.3% -0.3%
 12.9  99.5%  99.6% -0.1%
 13.0 100.0% 100.0% +0.0%
 13.1 100.5% 100.4% +0.1%
 13.2 101.0% 100.7% +0.3%
 13.3 101.5% 101.1% +0.4%
 13.4 102.0% 101.5% +0.5%
 13.5 102.5% 101.8% +0.7%
 13.6 103.0% 102.2% +0.8%
 13.7 103.5% 102.5% +1.0%
 13.8 104.0% 102.9% +1.1%
 13.9 104.5% 103.3% +1.2%
 14.0 105.0% 103.6% +1.4%
 14.1 105.5% 104.0% +1.5%
 14.2 106.0% 104.3% +1.7%
 14.3 106.5% 104.7% +1.8%
 14.4 107.0% 105.0% +2.0%
 14.5 107.5% 105.4% +2.1%
 14.6 108.0% 105.7% +2.3%
 14.7 108.5% 106.0% +2.5%
 14.8 109.0% 106.4% +2.6%
 14.9 109.5% 106.7% +2.8%
 15.0 110.0% 107.1% +2.9%
 15.1 110.5% 107.4% +3.1%
 15.2 111.0% 107.7% +3.3%
 15.3 111.5% 108.1% +3.4%
 15.4 112.0% 108.4% +3.6%
 15.5 112.5% 108.7% +3.8%
For 2 streets:
b = (s + 1)/5
with a useful range of about 1.1 ≤ s ≤ 4.5
Code:
   s     ≈      =     Δ
  1.0  40.0%  36.6% +3.4%
  1.1  42.0%  39.4% +2.6%
  1.2  44.0%  42.2% +1.8%
  1.3  46.0%  44.9% +1.1%
  1.4  48.0%  47.5% +0.5%
  1.5  50.0%  50.0% +0.0%
  1.6  52.0%  52.5% -0.5%
  1.7  54.0%  54.9% -0.9%
  1.8  56.0%  57.2% -1.2%
  1.9  58.0%  59.5% -1.5%
  2.0  60.0%  61.8% -1.8%
  2.1  62.0%  64.0% -2.0%
  2.2  64.0%  66.2% -2.2%
  2.3  66.0%  68.3% -2.3%
  2.4  68.0%  70.4% -2.4%
  2.5  70.0%  72.5% -2.5%
  2.6  72.0%  74.5% -2.5%
  2.7  74.0%  76.5% -2.5%
  2.8  76.0%  78.5% -2.5%
  2.9  78.0%  80.4% -2.4%
  3.0  80.0%  82.3% -2.3%
  3.1  82.0%  84.2% -2.2%
  3.2  84.0%  86.0% -2.0%
  3.3  86.0%  87.8% -1.8%
  3.4  88.0%  89.6% -1.6%
  3.5  90.0%  91.4% -1.4%
  3.6  92.0%  93.2% -1.2%
  3.7  94.0%  94.9% -0.9%
  3.8  96.0%  96.6% -0.6%
  3.9  98.0%  98.3% -0.3%
  4.0 100.0% 100.0% +0.0%
  4.1 102.0% 101.7% +0.3%
  4.2 104.0% 103.3% +0.7%
  4.3 106.0% 104.9% +1.1%
  4.4 108.0% 106.5% +1.5%
  4.5 110.0% 108.1% +1.9%
  4.6 112.0% 109.7% +2.3%
Beware that the above betting scheme may be fine for a bluff catcher vs polarized range toy game, but in real world poker, there are many more variables to consider. As long you keep this in mind when using this, some of you might sometimes find it useful at the table.

Last edited by R Gibert; 08-25-2016 at 07:31 PM.
Geometric Betting Math Quote
08-25-2016 , 08:42 PM
Quote:
For 2 streets:
b = (s + 1)/5
with a useful range of about 1.1 ≤ s ≤ 4.6
Code:
   s     ≈      =     Δ
  1.0  40.0%  36.6% +3.4%
  1.1  42.0%  39.4% +2.6%
  1.2  44.0%  42.2% +1.8%
  1.3  46.0%  44.9% +1.1%
  1.4  48.0%  47.5% +0.5%
  1.5  50.0%  50.0% +0.0%
  1.6  52.0%  52.5% -0.5%
  1.7  54.0%  54.9% -0.9%
  1.8  56.0%  57.2% -1.2%
  1.9  58.0%  59.5% -1.5%
  2.0  60.0%  61.8% -1.8%
  2.1  62.0%  64.0% -2.0%
  2.2  64.0%  66.2% -2.2%
  2.3  66.0%  68.3% -2.3%
  2.4  68.0%  70.4% -2.4%
  2.5  70.0%  72.5% -2.5%
  2.6  72.0%  74.5% -2.5%
  2.7  74.0%  76.5% -2.5%
  2.8  76.0%  78.5% -2.5%
  2.9  78.0%  80.4% -2.4%
  3.0  80.0%  82.3% -2.3%
  3.1  82.0%  84.2% -2.2%
  3.2  84.0%  86.0% -2.0%
  3.3  86.0%  87.8% -1.8%
  3.4  88.0%  89.6% -1.6%
  3.5  90.0%  91.4% -1.4%
  3.6  92.0%  93.2% -1.2%
  3.7  94.0%  94.9% -0.9%
  3.8  96.0%  96.6% -0.6%
  3.9  98.0%  98.3% -0.3%
  4.0 100.0% 100.0% +0.0%
  4.1 102.0% 101.7% +0.3%
  4.2 104.0% 103.3% +0.7%
  4.3 106.0% 104.9% +1.1%
  4.6 112.0% 109.7% +2.3%
  4.7 114.0% 111.2% +2.8%
Correcting an off-by-one-bug.
Geometric Betting Math Quote
10-05-2016 , 09:58 AM
at SPR 3 for 2 streets: 80% seems way off, it should be 66.6%
pot 100 SPR 3 Stack 300
300-80=220 stack left
80+80+100=260 potsize on next street
300-66.6=233.4
66.6+66.6+100=233.2
Geometric Betting Math Quote
10-05-2016 , 12:16 PM
Quote:
Originally Posted by shahrad
at SPR 3 for 2 streets: 80% seems way off, it should be 66.6%
pot 100 SPR 3 Stack 300
Flop: bet 80 --> now you have 220 chips.
Turn pot = 260 --> bet 80% = 208 --> Now you're all-in except for 12 chips (hence the exact answer is 82.3%).

(Btw, thanks R Gibert. Those approximation formulas may indeed be handy.)

If we try 66.6%...
Flop bet 66.6 --> Now you have 233.4 chips
Turn pot 233.34 --> bet 2/3 of that --> not even close to all-in
Geometric Betting Math Quote
10-15-2016 , 07:54 AM
What I urgently need is how to set up a river SPR 1 with two streets. As you guys can see I am not a mathematical genius so help very appreciated.
Geometric Betting Math Quote
02-02-2024 , 07:47 PM
Quote:
Originally Posted by shahrad
What I urgently need is how to set up a river SPR 1 with two streets. As you guys can see I am not a mathematical genius so help very appreciated.
That one is much easier - on the turn you bet a third of the effective stack minus a third of the pot. For example:

Effective Stack: $3000
Pot: $900

Which means on the turn we bet $700, creating a pot of $2300 with $2300 behind.
Geometric Betting Math Quote

      
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