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Why would Evaluate[] in Plot give me warning about precision?

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I have a code:-

Plot[Evaluate@PDF[NormalDistribution[1.6, 0.2], x], x, -6, 6]

And then I got the warning: General::munfl: Exp[-721.953] is too small to represent as a normalized machine number; precision may be lost. However, if I removed Evaluate, the warning disappears. Why would that? Would that matter?

I need to keep the Evaluate, since I am drawing various distributions.

Thanks in advance!

plotting evaluation machine-precision precision-and-accuracy

share|improve this question

asked Sep 20 at 3:39

H42H42

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2

$begingroup$

I have a code:-

Plot[Evaluate@PDF[NormalDistribution[1.6, 0.2], x], x, -6, 6]

And then I got the warning: General::munfl: Exp[-721.953] is too small to represent as a normalized machine number; precision may be lost. However, if I removed Evaluate, the warning disappears. Why would that? Would that matter?

I need to keep the Evaluate, since I am drawing various distributions.

Thanks in advance!

plotting evaluation machine-precision precision-and-accuracy

share|improve this question

asked Sep 20 at 3:39

H42H42

3,15722 silver badges1313 bronze badges

$endgroup$

add a comment
 | 

$begingroup$

I have a code:-

Plot[Evaluate@PDF[NormalDistribution[1.6, 0.2], x], x, -6, 6]

And then I got the warning: General::munfl: Exp[-721.953] is too small to represent as a normalized machine number; precision may be lost. However, if I removed Evaluate, the warning disappears. Why would that? Would that matter?

I need to keep the Evaluate, since I am drawing various distributions.

Thanks in advance!

plotting evaluation machine-precision precision-and-accuracy

share|improve this question

asked Sep 20 at 3:39

H42H42

3,15722 silver badges1313 bronze badges

$endgroup$

Plot[Evaluate@PDF[NormalDistribution[1.6, 0.2], x], x, -6, 6]

share|improve this question

asked Sep 20 at 3:39

H42H42

3,15722 silver badges1313 bronze badges

share|improve this question

asked Sep 20 at 3:39

H42H42

3,15722 silver badges1313 bronze badges

asked Sep 20 at 3:39

H42H42

3,15722 silver badges1313 bronze badges

asked Sep 20 at 3:39

H42H42

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1 Answer
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10

$begingroup$

When you use Evaluate, the PDF evaluates to an exponential:

pdf = PDF[NormalDistribution[1.6, .2], x]

1.99471 E^(-12.5 (-1.6 + x)^2)

When you evaluate this object with a large enough number x (on the order of 10), the resulting object is too small to represent as a machine number:

pdf /. x -> 10

General::munfl: Exp[-882.] is too small to represent as a normalized machine number; precision may be lost.

0.

Let's check. The smallest machine number is:

$MinMachineNumber

2.22507*10^-308

If we convert the pdf expression to one using extended precision numbers:

epdf = SetPrecision[pdf, 20];

and then evaluate epdf at 10:

epdf /. x->10

1.7870924971057366*10^-383

We see that the result is much smaller than the smallest possible machine number. This is why evaluating pdf at 10 produces an error message and Mathematica returns 0.

Now, when you remove the Evaluate, then Plot only evaluates the PDF object when it is numerical, and this doesn't produce any messages:

PDF[NormalDistribution[1.6, .2], 10]

1.787092497106*10^-383

Of course, the above output is not a machine number:

Precision @ PDF[NormalDistribution[1.6, .2], 10]

13.0095

If you are multiplying extremely small numbers with extremely large numbers, then setting the small numbers to zero can be an issue. In that case, it makes sense to work with extended precision numbers instead.

share|improve this answer

answered Sep 20 at 4:10

Carl WollCarl Woll

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10

$begingroup$

When you use Evaluate, the PDF evaluates to an exponential:

pdf = PDF[NormalDistribution[1.6, .2], x]

1.99471 E^(-12.5 (-1.6 + x)^2)

When you evaluate this object with a large enough number x (on the order of 10), the resulting object is too small to represent as a machine number:

pdf /. x -> 10

General::munfl: Exp[-882.] is too small to represent as a normalized machine number; precision may be lost.

0.

Let's check. The smallest machine number is:

$MinMachineNumber

2.22507*10^-308

If we convert the pdf expression to one using extended precision numbers:

epdf = SetPrecision[pdf, 20];

and then evaluate epdf at 10:

epdf /. x->10

1.7870924971057366*10^-383

We see that the result is much smaller than the smallest possible machine number. This is why evaluating pdf at 10 produces an error message and Mathematica returns 0.

Now, when you remove the Evaluate, then Plot only evaluates the PDF object when it is numerical, and this doesn't produce any messages:

PDF[NormalDistribution[1.6, .2], 10]

1.787092497106*10^-383

Of course, the above output is not a machine number:

Precision @ PDF[NormalDistribution[1.6, .2], 10]

13.0095

If you are multiplying extremely small numbers with extremely large numbers, then setting the small numbers to zero can be an issue. In that case, it makes sense to work with extended precision numbers instead.

share|improve this answer

answered Sep 20 at 4:10

Carl WollCarl Woll

98.1k44 gold badges133133 silver badges247247 bronze badges

$endgroup$

add a comment
 | 

10

$begingroup$

When you use Evaluate, the PDF evaluates to an exponential:

pdf = PDF[NormalDistribution[1.6, .2], x]

1.99471 E^(-12.5 (-1.6 + x)^2)

When you evaluate this object with a large enough number x (on the order of 10), the resulting object is too small to represent as a machine number:

pdf /. x -> 10

General::munfl: Exp[-882.] is too small to represent as a normalized machine number; precision may be lost.

0.

Let's check. The smallest machine number is:

$MinMachineNumber

2.22507*10^-308

If we convert the pdf expression to one using extended precision numbers:

epdf = SetPrecision[pdf, 20];

and then evaluate epdf at 10:

epdf /. x->10

1.7870924971057366*10^-383

We see that the result is much smaller than the smallest possible machine number. This is why evaluating pdf at 10 produces an error message and Mathematica returns 0.

Now, when you remove the Evaluate, then Plot only evaluates the PDF object when it is numerical, and this doesn't produce any messages:

PDF[NormalDistribution[1.6, .2], 10]

1.787092497106*10^-383

Of course, the above output is not a machine number:

Precision @ PDF[NormalDistribution[1.6, .2], 10]

13.0095

If you are multiplying extremely small numbers with extremely large numbers, then setting the small numbers to zero can be an issue. In that case, it makes sense to work with extended precision numbers instead.

share|improve this answer

answered Sep 20 at 4:10

Carl WollCarl Woll

98.1k44 gold badges133133 silver badges247247 bronze badges

$endgroup$

add a comment
 | 

$begingroup$

When you use Evaluate, the PDF evaluates to an exponential:

pdf = PDF[NormalDistribution[1.6, .2], x]

1.99471 E^(-12.5 (-1.6 + x)^2)

When you evaluate this object with a large enough number x (on the order of 10), the resulting object is too small to represent as a machine number:

pdf /. x -> 10

General::munfl: Exp[-882.] is too small to represent as a normalized machine number; precision may be lost.

0.

Let's check. The smallest machine number is:

$MinMachineNumber

2.22507*10^-308

If we convert the pdf expression to one using extended precision numbers:

epdf = SetPrecision[pdf, 20];

and then evaluate epdf at 10:

epdf /. x->10

1.7870924971057366*10^-383

We see that the result is much smaller than the smallest possible machine number. This is why evaluating pdf at 10 produces an error message and Mathematica returns 0.

Now, when you remove the Evaluate, then Plot only evaluates the PDF object when it is numerical, and this doesn't produce any messages:

PDF[NormalDistribution[1.6, .2], 10]

1.787092497106*10^-383

Of course, the above output is not a machine number:

Precision @ PDF[NormalDistribution[1.6, .2], 10]

13.0095

If you are multiplying extremely small numbers with extremely large numbers, then setting the small numbers to zero can be an issue. In that case, it makes sense to work with extended precision numbers instead.

share|improve this answer

answered Sep 20 at 4:10

Carl WollCarl Woll

98.1k44 gold badges133133 silver badges247247 bronze badges

$endgroup$

pdf = PDF[NormalDistribution[1.6, .2], x]

pdf /. x -> 10

$MinMachineNumber

epdf = SetPrecision[pdf, 20];

epdf /. x->10

PDF[NormalDistribution[1.6, .2], 10]

Precision @ PDF[NormalDistribution[1.6, .2], 10]

share|improve this answer

answered Sep 20 at 4:10

Carl WollCarl Woll

98.1k44 gold badges133133 silver badges247247 bronze badges

answered Sep 20 at 4:10

Carl WollCarl Woll

98.1k44 gold badges133133 silver badges247247 bronze badges

answered Sep 20 at 4:10

Carl WollCarl Woll

98.1k44 gold badges133133 silver badges247247 bronze badges