# Problem with Big Decimal - Calculation process slows down

**URL:** <https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144>\
**Category:** Coding Questions\
**Created:** [May 11, 2019, 11:37pm UTC](https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144 "2019-05-11T23:37:38Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![humayung](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/humayung/32/6089_2.png) [@humayung](https://discourse.processing.org/u/humayung)\
**Post date:** [May 11, 2019, 11:37pm UTC](https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144/1 "2019-05-11T23:37:38Z")

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Hey guys!  
i’m very new to Big Decimal  
i attempting to calculate mandelbrot set with high precision for ultra zoom capability, so i’m using Big Decimal to perform calculation.  
while calculating, the loop slows down. i suspected the problem is in BigDecimal method. looks like it performs a long decimal calculation, the decimal become bigger and bigger so it slowing down. but how is this happened? i have tried some ways like flooring it, but it couldn’t solve the problem

here the simplified codes:

```auto
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
MathContext mc = new MathContext(2, RoundingMode.FLOOR);

int maxIter = 100;

void setup() {
  BigDecimal x0 = new BigDecimal("2");
  BigDecimal y0 = new BigDecimal("1");
  BigDecimal x = new BigDecimal("0");
  BigDecimal y = new BigDecimal("0");

  int iteration = 0;   

  // the loop slowing down
  while (iteration < maxIter) {
    BigDecimal xTemp = x.multiply(x).subtract(y.multiply(y)).add(x0); // = xTemp = x*x - y*y + x0 : am i doing it right?
    y = x.multiply(y).multiply(new BigDecimal("2")).add(y0); // = y = x*y*2 + y0;
    x = xTemp;    
    //println(xTemp); // the decimal become bigger and bigger, it slows the process
    // the loop slowing down at ~22 loop
    println(iteration);
    iteration++;
  }  
  println("DONE!"); // this line should be executed
}

```

I have no clue how is this happened. Any help would be appreciated!

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<div class="post-metadata">

**Author:** ![morisil](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/morisil/32/6166_2.png) [@morisil](https://discourse.processing.org/u/morisil)\
**Post date:** [May 12, 2019, 8:46am UTC](https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144/2 "2019-05-12T08:46:20Z")

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Just instantiating `MathContext` will not apply it to any of the operations. It’s quite inconvenient, but you have to pass it every time again and again: e.g.: `new BigDecimal("2", mc)`, `x.multiply(x, mc)`, etc. You can also use `setScale` method on already instantiated `BigDecimal` instance.

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<div class="post-metadata">

**Author:** ![morisil](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/morisil/32/6166_2.png) [@morisil](https://discourse.processing.org/u/morisil)\
**Post date:** [May 12, 2019, 8:47am UTC](https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144/3 "2019-05-12T08:47:56Z")

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Overall scale and precision for BigDecimals might be confusing:

[http://www.piotrnowicki.com/2011/02/precision-and-scale-in-bigdecimal-and-mathcontext/](http://www.piotrnowicki.com/2011/02/precision-and-scale-in-bigdecimal-and-mathcontext/)

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<div class="post-metadata">

**Author:** ![humayung](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/humayung/32/6089_2.png) [@humayung](https://discourse.processing.org/u/humayung)\
**Post date:** [May 12, 2019, 11:06am UTC](https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144/4 "2019-05-12T11:06:37Z")

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Thanks @morisil, but i have tried `setScale` and `mc` before, that `MathContext` is from the complete code. i passed the `mc` to every calculation, and tried `setScale` but it remains the same. it is kinda weird, the xTemp pops out a long decimals.  
i tried something like this:

```auto
BigDecimal xTemp = x.multiply(x, mc).subtract(y.multiply(y, mc), mc).add(x0, mc).setScale(2, RoundingMode.HALF_DOWN);
y = x.multiply(y, mc).multiply(new BigDecimal("2", mc), mc).add(y0, mc).setScale(2, RoundingMode.HALF_DOWN)

```

am i doing it right?

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<div class="post-metadata">

**Author:** ![humayung](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/humayung/32/6089_2.png) [@humayung](https://discourse.processing.org/u/humayung)\
**Post date:** [May 12, 2019, 11:14am UTC](https://discourse.processing.org/t/problem-with-big-decimal-calculation-process-slows-down/11144/5 "2019-05-12T11:14:48Z")

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oh my gosh! i spot the mistake! silly me 😅

i forgot some spot on that complex plane can goes toward infinity. i have to test if it getting bigger and bigger.