Graph Sine Wave ... ?

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1.00/5 (2 votes)

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Hi ...
I've drawn up a code of sine wave :

C#

private double DegreeToRadian(double angle)
        {
            return Math.PI * angle / int.Parse(textBox3.Text);
        }

        private void Draw(double N)
        {
            int Yoffset = panel1.Height / 2;
            Graphics G = panel1.CreateGraphics();
            Pen P = new Pen(Color.Yellow, 1.5f);
            float x1, y1;
            for (double X = 0; X <= 360; X++)
            {
                x1 = (float)X;
                y1 = Yoffset + ((float)Math.Sin(DegreeToRadian(X * N)) * int.Parse(textBox2.Text));
                G.DrawRectangle(P, x1, y1, .5f, .5f);
            }
            P.Dispose();
        }

Then Button_Click :

C#

Draw(int.Parse(textBox1.Text));

Now I want ... How do I display the frequency in hertz?

Posted 23-Oct-14 5:28am

ghasem110deh

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Kenneth Haugland 23-Oct-14 12:21pm

I believe you will find what you need here:
http://en.wikipedia.org/wiki/Sine_wave

BillWoodruff 23-Oct-14 12:40pm

The frequency in Hertz is in textBox2 ? Where do you want to display the frequency ?

If the 'Draw method is called repeatedly, are you aware it could be speeded up by a factor of at least #100 ? Why aren't you using the Paint Event ?

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-10-23T10:20:00

Solution 3

Let's assume your sine function depends on time and its time domain is supposed to be infinite (time: −∞ to +∞). Then, if all 360° (2*π) of phase change takes time t, the frequency is 1/t.

Non-infinite time domains makes things quite complicated. If, for example, the function is zero (or any other constant value) everywhere except some fixed segment on the time axis, such as the segment depicted on your image, the spectrum will be continuous (and rather wide, in that case). It is calculated as Fourier transform https://en.wikipedia.org/wiki/Fourier_transform[^].

If the function is strictly periodical ("strictly" also implies infinite domain in time), the spectrum is discrete and is calculated as the Fourier series: https://en.wikipedia.org/wiki/Fourier_series[^].

Note that a spectrum consists of the points which are characterized not just with frequency, but frequency/phase, which, apparently also can be expressed as a complex number.

The case of the sine function on an infinite time domain I mentioned fist is just the special case of strictly periodic function, which is trivial and makes the discrete spectrum of just one line at the frequency 1/t and some phase.

—SA

Posted 23-Oct-14 10:20am

Sergey Alexandrovich Kryukov

Comments

[no name] 23-Oct-14 17:05pm

The only Thing I complain is, that you are using 360°....and while writing and reading the answer again I see 2π...ok, nothing to complain. A 5; even your answer most probably overtaxes OP. Regards, Bruno

Sergey Alexandrovich Kryukov 23-Oct-14 17:16pm

Thank you, Bruno.
As to degrees, I have more fundamental education than that when people pay too much attention for units and other conventional things. Folk wisdom says: if someone wakes you up and asks "what is the value of π?", appropriate canonical answer is: "a constant".
—SA

[no name] 23-Oct-14 17:42pm

I don't think that I pay to much attention for Units...and especially not for conventions. But for me _rad_ is the base for this things.

Sergey Alexandrovich Kryukov 23-Oct-14 17:44pm

Well, yes, of course, but can you explain why? :-)
—SA

[no name] 23-Oct-14 17:51pm

No, at least not in it's fundamental details ;) I can only reply what I learned. And what I remember it was hard to switch from basic school- knowledge about 0...360° to 0...2π afterwards. But I'm looking Forward for the Explanation ;)

Sergey Alexandrovich Kryukov 23-Oct-14 18:17pm

You naturally measure the angle as length of the arc divided by radius. In other words, this is length of the arc in the unit of radius, which makes is dimensionless, independent from radius (or any size factor). Nothing else can be a more natural measure of the angle.
—SA

[no name] 23-Oct-14 18:31pm

a.) Length of the arc: Ok there is the word "length" so I assume unit is something like [meter]

b.) Divided by radius...also I assume radius is [meter]

[meter] by [meter] is one....

Why somebody "invented" a unit rad for this?

Sergey, I'm really here to learn. Regards, Bruno

Sergey Alexandrovich Kryukov 23-Oct-14 19:16pm

There is no such thing as "rad". This is a measureless unit. Consider the word "radian" as a kind of historical jargon; in fact, this is the same thing as "1s" — cm/cm == 1, right? This is the whole idea: angle is a relative measure, dimensionless. Typically, mathematicians and physicist avoid using the word "radian". If something asks "what is that, degrees?", one may answer: "no; radians".

By the way, this is also a cultural thing. I noticed that you can spot a person having decent knowledge of zoology will try to avoid calling lion babies "cubs", preferring "kittens", which emphasizes understanding that this is the family Felidae, because animals from this family are collectively called "cats", not "animal relative to cats" (the usage associated with profanity). Likewise, use "radians" smells like thinking "this is something special, ooo-o, radians", but for the educated person this is nothing.

Did you hear because physicists avoid using standard SI system? Because it is pretty stupid. Physicists prefer cm/gram/second units. In theoretical physics, it's usual to use "Stanislavsky' system" (humorous term, everyone know who was Stanislavsky). Speed of light is the world constant, so let's consider C=1, dimensionless. Any speed can be measured in the units of C, dimensionless. Then, E=mc², so energy and mass can be measured in the same units, quantum energy is E=ћω, where ω is frequency, and ћ also can be considered 1. Therefore, the energy can be measured in inverse time units, as well as mass. The length can be measured in relative units, too, number of Plank's lengths. Now, force can measured in units m*a, int time units it will be (1/s)*(1/s*2)=1/(s³). Electricity and magnetism? The electron's charge is the universal constant, so consider it equal to 1. And so on. Historical constants go out of equations, without changing the meaning of those equations.

—SA

[no name] 23-Oct-14 19:43pm

Wow! I think it is worth to stay here to learn!! Thank you very much! But first I Need to understand your comment in Detail....and this is not a thing of a Minute ;)

:: Humorous term, everyone know who was Stanislavski
Everybody expect me :( ;)

Just sorting your comment...SI cm vs m is only 100 times...but let me first think about all the consequenses

Again, thanks. I will come back. Kind regards, Bruno

Sergey Alexandrovich Kryukov 23-Oct-14 20:06pm

Except you? No, I mean, after consulting Wikipedia. The expression is mostly Russian, where almost everyone understood who was that.
SI is different not only in unit scale. The number of units is different. Idiotic mole and candela, purely historical, first based on not understanding of atomic theory in chemistry, second based on not understanding light, excessive ampere, less fundamental than electric charge, excessive π factors in electromagnetic expressions...
—SA

BillWoodruff 23-Oct-14 19:26pm

+5 I enjoyed the semiotic deconstruction lecture immensely !

Sergey Alexandrovich Kryukov 23-Oct-14 19:31pm

Thank you, Bill.
—SA

[no name] 23-Oct-14 20:01pm

So you know Stanislavski ;P
;)