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Started programming on a ZX spectrum in the 80's and have moved through Assembly, Turbo Pascal, C++, C#, Fortran. My main area of focus is engineering and scientific computing like numerical methods and 3D graphics.


1d
comment Midpoint of the shortest distance between 2 rays in 3D
The vector from $a$ to $p$ projected onto the line is $b\left(\frac{b\cdot (p-a)}{b\cdot b}\right)$ and the above is another way of doing projections using the vector triple cross product.
1d
revised Midpoint of the shortest distance between 2 rays in 3D
added 491 characters in body
1d
answered Midpoint of the shortest distance between 2 rays in 3D
Nov
19
comment Ratio of Areas of Similar Triangles
The image link is broken for me.
Nov
10
comment Evaluate ${M\over2R^2}\int(R^2 - y^2)^{3\over2}dy$
The difficulty is the for a thin shell $\int dx = 0$, but $\int \rho dx >0$. Real mass density is infinite since the material volume of a hollow sphere is zero.
Nov
10
comment Evaluate ${M\over2R^2}\int(R^2 - y^2)^{3\over2}dy$
If real mass density $\rho$ is used then $w = \int \rho {\rm d}x$ Now the limits of this integration depend on $y$. To do this right your slicing has to be done with a polar angle ${\rm d}\theta$ instead of ${\rm d}y$. Then $dm = \rho \pi x^2 R d \theta d R$ instead of $dm=\rho \pi x^2 dx dy$
Nov
10
comment Evaluate ${M\over2R^2}\int(R^2 - y^2)^{3\over2}dy$
Dimensionally you integral is incorrect. The result should be of the mass times distance squared units.
Nov
10
answered Evaluate ${M\over2R^2}\int(R^2 - y^2)^{3\over2}dy$
Nov
10
comment Evaluate ${M\over2R^2}\int(R^2 - y^2)^{3\over2}dy$
I think your $dm$ is suspeect. If you do $\int dm = \int \frac{M \sqrt{R^2-y^2}}{2 R^2}\,{\rm d}y = \frac{\pi}{8} M R \ne M$. Shouldn't by definition $M=\int dm$?
Nov
10
comment Evaluate ${M\over2R^2}\int(R^2 - y^2)^{3\over2}dy$
Moment of inertia calculation should not have a fractional exponent. Can you show more of how you arrived at this.
Nov
9
awarded  Yearling
Nov
5
comment Solving a matrix equality
I don't think you know $D$ unless you know what $X$ is.
Nov
5
comment Solving a matrix equality
Yes. Also I think \top works better that T for the transpose symbol.
Nov
5
comment Solving a matrix equality
I think the most general problem is $$A X + B X^\top + C =0$$
Nov
5
comment Solving a matrix equality
Do you know the shapes of the matrices (if rows are less, equal or more than the columns)?
Oct
25
comment How to identify the surface of a cylindrical patch?
Is it a finite cylinder (for computer graphics) or an infinite cylinder (for mathematics)?
Oct
24
comment Equal time path
NOTE: This question arose from the comments of math.stackexchange.com/q/989423/3301
Oct
24
comment Time it takes a mass point to go down a curve under gravity
This is not an effective use of Mathematics. Please post a new question with the new problem.
Oct
24
comment Time it takes a mass point to go down a curve under gravity
What is your question here? With this problem, if you parametrize a curve you can find the parameters that will yield the given time $T$. It is the same answer, even though you are changing the question now.
Oct
24
comment Time it takes a mass point to go down a curve under gravity
The time is in there, you must have missed it. See my answer now.