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Plot results of Fermat factorization method with ContourPlot?

For the following set of commands the Contour Plot does not appear to display:

h = Cos[(2 \[Pi] ((x)^2 + (y)^2)/(2*5*w))]^2

h1
u1 = ContourPlot[h1 == 1, {x, -15, +15}, {y, -15, +15}, 
   GridLines -> Automatic];
u2 = Graphics[{Red, Point[{7, 11}]}];
s4 = Show[{u1, u2}]

Plot3D[h1, {x, -15, +15}, {y, -15, +15}]

The complete NoteBook is attached. You insights are welcome.

I'm using Version 11.3

Regards, Edward

Attachments:
POSTED BY: Edward Newsome
5 Replies

It looks very cool.

Sure. Just for the logs, ContourPlot[] must not be used where it does not fit

Clear[h, h1, h1r]
h[x_, y_, w_] := Cos[2 \[Pi] (x^2 + y^2)/(2 5 w)]^2
h1[x_, y_] := h[x, y, 17.]
h1r[r_] := Cos[2 \[Pi] r^2/170.]^2

combine three different 2D graphics into one plot

Show[{ContourPlot[h1[x, y], {x, -15, 15}, {y, -15, 15},
   Contours -> 10, 
   ColorFunction -> "Pastel",
   PlotLegends -> Automatic,
   DisplayFunction -> Identity],
  ParametricPlot[(# {Cos[\[Phi]], Sin[\[Phi]]}) & /@ 
    Sqrt[85. Range[5]], {\[Phi], 0, 2 \[Pi]},
   PlotStyle -> {Black, Dashed},
   DisplayFunction -> Identity], 
  Graphics[{Black, Point[{0, 0}],
    DisplayFunction -> Identity}]},
 DisplayFunction -> $DisplayFunction]

as

enter image description here

POSTED BY: Dent de Lion

Thanks for the recommendations. First, as pointed out by Dent de Lion:

(1) Contours for functions f(x,y) = 0 where f(x,y) >= 0 are always poorly detected

Second, I needed to develop a better understanding of the "ContourPlot" function.

Lastly, to show you the final form of my script or program, I have attached the Notebook with the correct utilization of the "ContourPlot" function. The graphic output meets my visualization objectives.

I like it. It looks very cool. Again, thanks for the recommendations.

Attachments:
POSTED BY: Edward Newsome

Contour Plot -- Not Displaying

because one has to deliver variables in the plot functions which relate to the variables given in the domain specification of the plot. For all explicit plot functions the variables must be the same, so

Clear[h, h1]
h[x_, y_, w_] := Cos[2 \[Pi] (x^2 + y^2)/(2 5 w)]^2
h1[x_, y_] := h[x, y, 17.]

then still you don't see an output with

ContourPlot[h1[x, y]==1, {x, -15, 15}, {y, -15, 15},GridLines -> Automatic]

despite

In[54]:= FindInstance[1/170 (x^2 + y^2) == 1, {x, y}, Reals, 3] // N
Out[54]= {{x -> 9.5, y -> 8.93029}, {x -> -10.3333, y -> -7.95124}, {x -> 3.25, y -> 12.6269}}

the request has a meaningful domain. If you mouse over

ContourPlot[h1[x, y], {x, -15, 15}, {y, -15, 15}, Contours -> 10]

you see value 1 is not caught. In the manual ContourPlot is a hint

Contours  for functions f(x,y) = 0 where f(x,y) >= 0 are always poorly detected

This is the case here (for h1[x,y]==1 where h1[x,y]<=1).

This works

Plot3D[h1[x, y], {x, -15, 15}, {y, -15, 15}, PlotPoints -> {31, 39}]
POSTED BY: Dent de Lion

Cool, Udo.

I think this is nice as well

Show[Plot3D[h1[x, y], {x, -15, 15}, {y, -15, 15}, PlotPoints -> {31, 39}], 
 Plot3D[.95, {x, -15, 15}, {y, -15, 15}, PlotStyle -> Opacity[.8]]]

and your statement slightly modified

ContourPlot[h1[x, y] == .95, {x, -15, 15}, {y, -15, 15},  GridLines -> Automatic]
POSTED BY: Hans Dolhaine
Posted 5 years ago

Your commands above do not seem to hang together as a complete set. You define h, which is not then used (did you mean h1?).

In the next line, you have h1 u1 = ...

Are h1 and u1 supposed to be multiplied together? If so, why are you then assigning to them (with a single = sign) as though they were a variable? What does this mean?

You seem to be using h1 as a function, taking parameters x and y. But in that case, should you not define it by, say

h1[x_, y_] := Cos[(2[Pi] ((x)^2 + (y)^2)/(25 w))]^2

From what I can tell, you seem to have a number of confusions. I suggest you look at some examples of ContourPlot and gradually adapt them towards what you want.

POSTED BY: Marc Widdowson
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