Formula Error?

[YuNoMad?]

What is it you are trying to achieve?
To graph an equation y = 2x -3 on a graph when x is -20 to 20 by an increment of 1 each time


What is the problem you are having?
The graphed line will not appear on the screen or if it does it stops after one segment

Describe what you have tried to solve this problem
I have tried fixing this by changing what x is and it still isn't working, but since my teacher doesn't really teach us he just posts tutorials from this site, I don't know how to fix it. Also, I tried making the boxes that get drawn larger by 1000 pixels and they barely show up in the top left

Post any relevant code

Turing:

var xx, yy : int i := -1     xx := (version one was the formula -20 * 15 + 335, version two I tried simply putting 200)     yy := 2 * xx - 3     loop         i := i + 1         delay (5)         drawfillbox (xx - 2, yy - 2, xx + 2, yy +2, 2)         drawline (xx, yy, xx + 15, yy + 15, 2)         xx := (-20 + i) * 15 + 335         yy := 2 * x - 3         exit when i = 40     end loop

Please specify what version of Turing you are using
At school I'm not sure what version we use but at home I use 4.1.1

[RandomLetters]

It's working for me, it draws green squares with segments attached to them.
Are you trying to connect them as one line?

Turing:

var xx, yy : int var i := -1 xx := 20 * 15 + 335 yy := 2 * xx - 3 loop     i := i + 1     delay (5)     drawfillbox (xx - 2, yy - 2, xx + 2, yy + 2, 2)     drawline (xx, yy, xx + 15, yy + 15, 2)     xx := (-20 + i) * 15 + 335     yy := 2 * xx - 3     exit when i = 40 end loop

[Zren]

You can ignore the top bit, but seeing as your teach is...
You can learn more about functions and subroutines in the Turing Walkthrough.

Turing:

% y = 2x-3 % f(x) = 2x-3 % First off, if you haven't learnd functions in math+compsci yet, this 'll make % it easier to read, and change the formula later. % The basics of it are %   1    2    3         4 function f (x : int) : int     %  5      6     result 2 * x - 3     %  7 end f % 1: Declare the next block of code is part of a function. All the way to 7. % 2: The name of the function. Must be unique. % 3: Local variables that can only be used within the function. Sort of like %    with the varibles you use in loops. % 4: This function must return (be equal to) something when you call it. In %    this example, we return a number. % 5: Since a function must return something, we have to have some way to tell %    what that is. % You can also have other bits of code and other local variables. function anotherF (x : int) : int     var y := 2 * x - 3     result y end anotherF % Using the function. It returns a number to be printed. put f (42)

Now onto your assumed problem. Where the graph goes way offscreen. You need to scale it. More precisely, you need to scale the numbers you calculate of the equation to be used for the coordinates.

Turing:

function f (x : int) : int     result 2 * x - 3 end f % Originally just drawing points at the coordinates on the screen. for x : 0 .. maxx     Draw.Dot (x, f (x), black) end for % Find the highest y coordinate in the range used of the function. var gMaxY := 0 for x : 0 .. maxx     var y := f (x)     if y > gMaxY then         gMaxY := y     end if end for % We want to scale the graph so that the top of the screen is the highest point. % To do that, we want each pixel on the screen to represent more than one unit. % Like when you have a dash count for 2 or 5 in a graph on paper. To how much % we count by, we divide the number of dashes we'd have (in this case, pixels), % with the maximum number we desire. var scaleY := maxy / gMaxY % Then we scale all the points by that ratio. for x : 0 .. maxx     Draw.Dot (x, round (f (x) * scaleY), red) end for

That was either overkill, or completely off the mark. Oh well.

[YuNoMad?]

if I had the time I would throw out what I have now and start over with functions, but I need it finished tomorrow so I'm going to change it up a bit as I have it below. it's uncommented, sorry, don't have the time >.> (two projects and this for tomorrow)

Turing:

var i, xx, yy : int procedure progi i := -9     xx := -10 * 15 + 335     yy := (2 * -10 - 3) * 15 + 335     loop         i := i + 1         delay (50)         drawfillbox (xx - 2, yy - 2, xx + 2, yy + 2, 2)         drawline (xx, yy, (i + 1) * 15 + 335, (2 * (i + 1) - 3) * 15 + 335, 2)         xx := i * 15 + 335         yy := (2 * i - 3) * 15 + 335         exit when i = 11     end loop     drawfillbox (xx - 2, yy - 2, xx + 2, yy + 2, 2) end progi

the drawline code is just to go through to the next step of the formula and draw a line to there.


The next step of this program is to use a "sin(x)" and I know that has to do with wavelengths but we haven't learnt those yet and I don't know how to convert my xx to something that can be used in a sin, or vice versa, and still be graphed in pixel graphics.

Here is what I have now:

Turing:

var xx3, yy3 : int procedure progiv     xx3 := -20 * 15 + 335     yy3 := sin (xx3)     loop         drawfillbox (xx3 - 2, yy3 - 2, xx3 + 2, yy3 + 2, 2)         drawline (xx3, yy3, xx3 + 15, yy3 + 15, 2)         xx3 := xx3 + 15         yy3 := xx3         exit when xx >= 640     end loop     drawfillbox (xx - 2, yy - 2, xx + 2, yy + 2, 2) end progiv

should I make a yy3r/xx3r as reals to be used in a sin and round them into ints?

[Zren]

> should I make a yy3r/xx3r as reals to be used in a sin and round them into ints?

Yes.

Just so you know, sin() returns fractions from 0 .. 1. Eg: 0.745113. You might need to scale the number up a bit before rounding it.

[YuNoMad?]

is there anything else specific I should know about sins before attempting to use them in a program, such as limit to the input?

this is what I am going to end up using, but my lines that I'm trying to draw from dot to dot are going off on some odd tangent. why is this?

Turing:

var y1, yy3, xx3 : int var yyy3 : real procedure progiv     i := -20     xx3 := -20 * 15 + 335     yyy3 := sin (i)     yy3 := (round (sin (i)) * 15 + 335     y1 := yy3     yy3 := (round (sin (i + 1))) * 15 + 335     loop         i := i + 1         drawline (xx3, y1, i * 15 + 335, (2 * yy3 - 3) * 15 + 335, 5)         yyy3 := sin (i)         yy3 := (round (yyy3)) * 15 + 335         drawfillbox (xx3 - 2, yy3 - 2, xx3 + 2, yy3 + 2, 5)         xx3 := xx3 + 15         exit when i = 20         y1 := yy3     end loop     drawfillbox (xx3 - 2, yy3 - 2, xx3 + 2, yy3 + 2, 5) end progiv

Fixed. I accidentally accounted for the scale of pixel to graph twice.