     POV-Ray : Newsgroups : povray.advanced-users : Exponential cylinder density function Server Time 6 May 2021 15:26:29 EDT (-0400) Exponential cylinder density function (Message 1 to 8 of 8)         From: Mike Horvath Subject: Exponential cylinder density function Date: 6 Feb 2021 23:48:34 Message: <601f7122\$1@news.povray.org>    ```I am using this density function:

function {1-f_cylindrical(x,y,z)}

How do I make it so that the density decreases exponentially?

Simply this?

function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}

Thanks.

Mike
```    From: Mike Horvath Subject: Re: Exponential cylinder density function Date: 6 Feb 2021 23:49:50 Message: <601f716e\$1@news.povray.org>    ```On 2/6/2021 11:48 PM, Mike Horvath wrote:
> I am using this density function:
>
> function {1-f_cylindrical(x,y,z)}
>
> How do I make it so that the density decreases exponentially?
>
> Simply this?
>
> function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}
>
> Thanks.
>
>
> Mike

Increases rather.

Mike
```    From: Bald Eagle Subject: Re: Exponential cylinder density function Date: 7 Feb 2021 09:10:09 Message:    ```Mike Horvath <mik### [at] gmail com> wrote:
> On 2/6/2021 11:48 PM, Mike Horvath wrote:
> > I am using this density function:
> >
> > function {1-f_cylindrical(x,y,z)}
> >
> > How do I make it so that the density decreases exponentially?
> Increases rather.

> > function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}

This would be geometrically?

Exponentially would imply using log() or (exp) ?
or maybe pow (term, some varying power)

I usually use a spreadsheet, or plot my function in POV-Ray with spheres to show
myself what's actually going on
```    From: Alain Martel Subject: Re: Exponential cylinder density function Date: 8 Feb 2021 10:24:57 Message: <602157c9\$1@news.povray.org>    ```Le 2021-02-07 à 09:07, Bald Eagle a écrit :
>
> Mike Horvath <mik### [at] gmail com> wrote:
>> On 2/6/2021 11:48 PM, Mike Horvath wrote:
>>> I am using this density function:
>>>
>>> function {1-f_cylindrical(x,y,z)}
>>>
>>> How do I make it so that the density decreases exponentially?
>> Increases rather.
>
>
>>> function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}
>
> This would be geometrically?
>
> Exponentially would imply using log() or (exp) ?
> or maybe pow (term, some varying power)
>
> I usually use a spreadsheet, or plot my function in POV-Ray with spheres to show
> myself what's actually going on
>
>

function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}
is exactly the same as
function {1-pow(f_cylindrical(x,y,z),2)}

The advantage of the second is that f_cylindrical need to be evaluated
only once, making the evaluation of the whole function faster.

An exponential curve could be something like :
function {1- exp(f_cylindrical(x,y,z))}
```    From: Mike Horvath Subject: Re: Exponential cylinder density function Date: 8 Feb 2021 16:22:25 Message: <6021ab91\$1@news.povray.org>    ```On 2/7/2021 9:07 AM, Bald Eagle wrote:
> This would be geometrically?
>

Dunno what you mean.

> Exponentially would imply using log() or (exp) ?
> or maybe pow (term, some varying power)
>
> I usually use a spreadsheet, or plot my function in POV-Ray with spheres to show
> myself what's actually going on
>
>

Which would be better for planet atmosphere density? I used `pow` but is
`exp` better?

Mike
```    From: Mike Horvath Subject: Re: Exponential cylinder density function Date: 8 Feb 2021 16:24:04 Message: <6021abf4\$1@news.povray.org>    ```On 2/8/2021 10:24 AM, Alain Martel wrote:
> The advantage of the second is that f_cylindrical need to be evaluated
> only once, making the evaluation of the whole function faster.
>

Good tip, thanks! Any speed improvement is important.

Mike
```    From: Bald Eagle Subject: Re: Exponential cylinder density function Date: 8 Feb 2021 18:55:01 Message:    ```Mike Horvath <mik### [at] gmail com> wrote:
> On 2/7/2021 9:07 AM, Bald Eagle wrote:
> > This would be geometrically?
> Dunno what you mean.

Doesn't matter - I think they're the same.

> Which would be better for planet atmosphere density? I used `pow` but is
> `exp` better?

https://en.wikipedia.org/wiki/Density_of_air#Variation_with_altitude
```    From: Mike Horvath Subject: Re: Exponential cylinder density function Date: 22 Feb 2021 13:57:50 Message: <6033feae\$1@news.povray.org>    ```On 2/8/2021 6:52 PM, Bald Eagle wrote:
> Mike Horvath <mik### [at] gmail com> wrote:
>> On 2/7/2021 9:07 AM, Bald Eagle wrote:
>>> This would be geometrically?
>> Dunno what you mean.
>
> Doesn't matter - I think they're the same.
>
>
>> Which would be better for planet atmosphere density? I used `pow` but is
>> `exp` better?
>
> https://en.wikipedia.org/wiki/Density_of_air#Variation_with_altitude
>
>
>
>

I'm not very good at math so I don't know how to translate that into
something POV-Ray can consume.

Mike
```        