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PODrag value in simulation blows up and then NaN
 

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  1. PODrag value in simulation blows up and then NaN
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    <p>I'm writing a "physics simulation" (so to speak) where using the keyboard arrows one applies forces to a sphere. In this latest iteration I added drag, like the sphere is in the air. Then, for certain values, the drag calculation starts to blow up! The number gets too big, and then Infinity and right after that NaN (cause of the Infinity / Infinity division).</p> <p>You can see it happening here: <a href="http://gool.jit.su/the-drag" rel="nofollow noreferrer">http://gool.jit.su/the-drag</a>. Open the console and start moving, left or right. In a few seconds it breaks. You can see in the console the drag value being logged until right before it becomes NaN. (we have a great force and a very small mass)</p> <p>I'm really trying to understand what is happening and why it is happening, but perhaps there are already information on similar problemas that I was unable to find out or some sort of best practice to keep the number under control... Perhaps choose a value to be my MAX and test agains it every time...</p> <p>Any idea, help and suggestion is very welcome. I think I am about to learn something important, but still needing a push in the right direction. :)</p> <p><strong>UPDATE 2</strong>: @Beta's test (sorta)</p> <p>After @Beta's comment I did this test and indeed his calculations seems to show where my simulation breaks apart. (console log velocity in the x axis when the test returns true, false otherwise)</p> <p><img src="https://i.stack.imgur.com/waj5k.png" alt="enter image description here"></p> <p><strong>UPDATE 1</strong>: Some code</p> <p>Most "physics" happen here:</p> <pre><code>update: function update(k, dt) { var up = k.UP, right = k.RIGHT, down = k.DOWN, left = k.LEFT; up = up &amp;&amp; -this.output; right = right &amp;&amp; this.output; down = down &amp;&amp; this.output; left = left &amp;&amp; -this.output; this.force.x = left + right; this.force.y = up + down; this.calculate_drag(this.velocity); if (!isNaN(this.drag.x)) { console.log(this.drag); } // this.net_force.x = this.force.x; // this.net_force.y = this.force.y; this.net_force.x = this.force.x + this.drag.x; this.net_force.y = this.force.y + this.drag.y; this.acceleration.x = this.net_force.x / this.mass; this.acceleration.y = this.net_force.y / this.mass; this.velocity.x += this.acceleration.x / (1000 / dt); this.velocity.y += this.acceleration.y / (1000 / dt); this.momentum.x = this.mass * this.velocity.x; this.momentum.y = this.mass * this.velocity.y; this.position.x += (this.velocity.x * global.METRE) / (1000 / dt); this.position.y += (this.velocity.y * global.METRE) / (1000 / dt); this.energy += (abs(this.net_force.x) + abs(this.net_force.y)) / (1000 / dt); } </code></pre> <p>And here:</p> <pre><code>calculate_drag: function calculate_drag() { var c = 0.47, a = PI * this.radius * this.radius, rho = 1.22, direction = function direction(velocity) { if (velocity === 0) { return 1; } return velocity / abs(velocity); }; this.drag.x = -0.5 * c * a * rho * this.velocity.x * this.velocity.x * direction(this.velocity.x); this.drag.y = -0.5 * c * a * rho * this.velocity.y * this.velocity.y * direction(this.velocity.y); } </code></pre> <p>Both methods of gPrototype in gee.js.</p>
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    1. COI tried to read your code, but it is very confusing. You are mixing physical model with UI, you have lots of global variables and you attach some new variables to DOM elements. Can you show us just the "physics part"?
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      1. USIvan Kuckir
    2. COYou are also using 3 JS libraries, which tweak the standard DOM behavior. E.g. what is Date.now() ?
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      1. USIvan Kuckir
    3. CO@IvanKuckir Well, the only important part, I think, is in gee.js. The gPrototype is the object. I will update the question. Thanks.
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