@mmcdara Thanks for you points and links.  It was only a very general case, and not time dependent, basically a blanket generalization - as t approaches infintiy the total number of people sick is 30%.  As you mention we could include many time dependencies such as but not limited to, time of exposure, time of incubation, time sick but not infectious, time not sick but infectious etc..

It would be interesting to see someone come up with a model like you describe, actually I came across this 2D covid visualization simulation which would make a great maple application https://pongcenter.itch.io/anti-plague linked from this article https://www.frontiersin.org/articles/10.3389/fcomp.2021.642321/full#SM1 (Simulation Agent-Based Model to Demonstrate the Transmission of COVID-19 and Effectiveness of Different Public Health Strategies)

In the meantime I'll check out the links you mention, I've got a bit of reading to do.

@Carl Love  Great! Thanks that's it.

Mapleflow ends with = and it automatically enters 1.  One of the minor differences from Maple.

Very insightful, thanks all.

@ccAndrew actually I did locate a 2016 answer.  I would like to be able to cycle through his posts, but I cannot since his user account in mapleprimes doesn't appear to be working.

@Valerie I'm not sure if I'm getting the right output.  Can you show your input and output signals here?  I would also, if possible, like to see a visual simulation of the box and mass.

Masking is I suppose not the correct term.  More or less a notch filter I think is what it is. 

In the clown example the trouble is how to get this but I think what has been left out was that it was loaded in an editor (paint) and red circles were manually applied and saved as a seperate file, loaded back in and from there extracted a difference image against the unedited version.  

What I found on the web was this

Please present a reference

Regarding the screen angle I think it has something to do with gamma correction.  I don't know if that has anything to do with blocking certain colors but if I tilt the screen, more and more red is blocked and we see more green and blue, at least on some monitors.  I think I can simulate the colors I see be reducing the red channel in the image.  The gamma correction controls the brightness so maybe yes changing the brightness of the color channel is in effect changing the gamma.

With my laptop as the lid is closed the colors at a steep angle change (white becomes black, light greys stay white etc..)  I am trying to replicate the colors you see when you look at a steep angle on a screen.

The windows logo looks slightly different on an angle and I thought it was a color inversion or negative.  Is there any way to replicate those steep angle colors?

@acer I didn't know a color inversion was the same thing as a negative, but that makes sense. 

There is an illusion in the windows logo which I am trying to replicate.

How about an image negative?

@Acer Yes, I think.  I also found these other two ways that do the same thing

Using the windows 7 background desktop as the image

with(ImageTools):

img:=Read("c:/Windows/Web/Wallpaper/Windows/img0.jpg):
img1:=evalf(map(x->(1-x),img)):View(img1)

I also found another way to display the same thing

img2:=FitIntensity(img,1..0):
View(img2)

Here's code for two different ways to animate the graph

with(plots):
animate(plot,[x²+t,x=-2..2],t=0..1);

and the second way

with(plots):
display(seq(plot(x²+t/20,x=-2..2),t=0..20),insequence=true);

The new application center useability borders on the unuseable for dial up users.  Currently I'm on dial-up and the initial page of the application center has been loading for, oh ... I'd say about 10 minutes now and its. ... still loading.  Why do they need hi res pictures, can't they downgrade them? It'll definitely speed things up.  Anyone with a dial-up connection will find the center almost unbearable and unbelievably slow compared to the ultra fast application center of old. 

Maybe a poll should be done on high speed and dial up internet connections just to find out what percentage of users are on high speed.  I may be on the low side but probably not for long, the sinking economy will bring people back down to earth.  Job losses today and tomorrow are surely going to have people cutting their high speed high priced internet connections from their bills everymonth to save money.  Luckily, for now, I can use the high speed T1 line at work and even there I noticed it fairly slow. 

Adding a classic site interface like maple itself would solve the speed issue immediately and give users an option.