Appendix/Ramblings/T6CoordinatesPt2

Concentric Ellipsoidal (T6) Coordinates (Part 2)

Orthogonal Coordinates

Speculation5

Spherical Coordinates

$r\cos \theta$	$=$	$z,$
$r\sin \theta$	$=$	$(x^2+y^2{)}^{1/2},$
$\tan \phi$	$=$	$\frac{y}{x}.$

Use λ₁ Instead of r

Here, as above, we define,

${\lambda }_1^2$

$\equiv$

$x^2+q^2{y}^2+p^2{z}^2$

Using this expression to eliminate "x" (in favor of λ₁) in each of the three spherical-coordinate definitions, we obtain,

$r^2\equiv x^2+y^2+z^2$	$=$	${\lambda }_1^2-y^2(q^2-1)-z^2(p^2-1);$
${\tan }^2\theta \equiv \frac{x^2+y^2}{z^2}$	$=$	$\frac{1}{z^2}[{\lambda }_1^2-y^2(q^2-1)-p^2{z}^2];$
$\frac{1}{{\tan }^2\phi }\equiv \frac{x^2}{y^2}$	$=$	$\frac{{\lambda }_1^2-p^2{z}^2}{y^2}-q^2.$

After a bit of additional algebraic manipulation, we find that,

$\frac{z^2}{{\lambda }_1^2}$	$=$	$\frac{(1+{\tan }^2\phi )}{{{𝒟}}^2},$
$\frac{y^2}{{\lambda }_1^2}$	$=$	$\left[\frac{{{𝒟}}^2{\tan }^2\phi -p^2{\tan }^2\phi (1+{\tan }^2\phi )}{(1+q^2{\tan }^2\phi ){{𝒟}}^2}\right],$
$\frac{x^2}{{\lambda }_1^2}$	$=$	$1-q^2\left(\frac{y^2}{{\lambda }_1^2}\right)-p^2\left(\frac{z^2}{{\lambda }_1^2}\right),$

where,

${{𝒟}}^2$

$\equiv$

$[(1+q^2{\tan }^2\phi )(p^2+{\tan }^2\theta )-p^2(q^2-1){\tan }^2\phi ].$

As a check, let's set $q^2=p^2=1$, which should reduce to the normal spherical coordinate system. ${\lambda }_1^2$ $\to$ $r^2,$       and,       ${{𝒟}}^2$ $\to$ $[(1+{\tan }^2\phi )(1+{\tan }^2\theta )].$ $\Rightarrow \frac{z^2}{{\lambda }_1^2}$ $\to$ $\frac{1}{1+{\tan }^2\theta }={\cos }^2\theta =\frac{z^2}{r^2};$ $\frac{y^2}{{\lambda }_1^2}$ $\to$ $\left[\frac{(1+{\tan }^2\phi )(1+{\tan }^2\theta ){\tan }^2\phi -{\tan }^2\phi (1+{\tan }^2\phi )}{(1+{\tan }^2\phi )(1+{\tan }^2\phi )(1+{\tan }^2\theta )}\right]$   $=$ $\frac{{\tan }^2\phi }{(1+{\tan }^2\phi )}\left[\frac{{\tan }^2\theta }{(1+{\tan }^2\theta )}\right]={\sin }^2\theta {\sin }^2\phi =\frac{y^2}{r^2};$ $\frac{x^2}{{\lambda }_1^2}$ $\to$ $1-\left(\frac{y^2}{{\lambda }_1^2}\right)-\left(\frac{z^2}{{\lambda }_1^2}\right),$   $\to$ $1-{\sin }^2\theta {\sin }^2\phi -{\cos }^2\theta =-{\sin }^2\theta {\sin }^2\phi +{\sin }^2\theta ={\sin }^2\theta {\cos }^2\phi =\frac{x^2}{r^2}.$

Relationship To T3 Coordinates

If we set, $q=1$, but continue to assume that $p>1$, we expect to see a representation that resembles our previously discussed, T3 Coordinates. Note, for example, that the new "radial" coordinate is,

${\lambda }_1^2$

$\to$

$({\varpi }^2+p^2{z}^2),$

and,

${{𝒟}}^2$

$\to$

$[(1+{\tan }^2\phi )(p^2+{\tan }^2\theta )].$

$\Rightarrow \frac{p^2{z}^2}{{\lambda }_1^2}$	$\to$	$\frac{p^2}{(p^2+{\tan }^2\theta )}=\frac{1}{(1+p^{-2}{\tan }^2\theta )},$
$\frac{{\varpi }^2}{{\lambda }_1^2}=\frac{x^2}{{\lambda }_1^2}+\frac{y^2}{{\lambda }_1^2}$	$\to$	$1-p^2\left(\frac{z^2}{{\lambda }_1^2}\right)=[1-\frac{1}{(1+p^{-2}{\tan }^2\theta )}].$

We also see that,

$\frac{{\varpi }^2}{p^2{z}^2}$

$\to$

$(1+p^{-2}{\tan }^2\theta )[1-\frac{1}{(1+p^{-2}{\tan }^2\theta )}]=p^{-2}{\tan }^2\theta .$

Again Consider Full 3D Ellipsoid

Let's try to replace everywhere, $[\varpi /(pz){]}^2=p^{-2}{\tan }^2\theta$ with ${\lambda }_2$. This gives,

$\frac{{{𝒟}}^2}{p^2}$

$\equiv$

$[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ].$

which means that,

$\frac{p^2{z}^2}{{\lambda }_1^2}$	$=$	$\frac{(1+{\tan }^2\phi )}{[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}$
	$=$	$\frac{(1+{\tan }^2\phi )/{\tan }^2\phi }{[q^2{\lambda }_2(1+q^2{\tan }^2\phi )/(q^2{\tan }^2\phi )-(q^2-1)]}=\frac{1/{\sin }^2\phi }{[q^2{\lambda }_2{Q}^2-(q^2-1)]},$
$\frac{q^2{y}^2}{{\lambda }_1^2}$	$=$	$\frac{q^2{\tan }^2\phi }{(1+q^2{\tan }^2\phi )}-\frac{q^2{\tan }^2\phi (1+{\tan }^2\phi )}{(1+q^2{\tan }^2\phi )[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}$
	$=$	$\frac{q^2{\tan }^2\phi }{(1+q^2{\tan }^2\phi )}\{1-\frac{(1+{\tan }^2\phi )}{[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}\}$
	$=$	$\frac{q^2{\tan }^2\phi }{(1+q^2{\tan }^2\phi )}\{1-\frac{(1+{\tan }^2\phi )/{\tan }^2\phi }{[q^2{\lambda }_2(1+q^2{\tan }^2\phi )/(q^2{\tan }^2\phi )-(q^2-1)]}\}$
	$=$	$\frac{1}{Q^2}\{1-\frac{1/{\sin }^2\phi }{[q^2{\lambda }_2{Q}^2-(q^2-1)]}\}=\frac{1}{Q^2[]}[[]-\frac{1}{{\sin }^2\phi }],$
$\frac{x^2}{{\lambda }_1^2}$	$=$	$1-\frac{q^2{\tan }^2\phi }{(1+q^2{\tan }^2\phi )}\{1-\frac{(1+{\tan }^2\phi )}{[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}\}$
		$-\frac{(1+{\tan }^2\phi )}{[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}$
	$=$	$1-\frac{q^2{\tan }^2\phi }{(1+q^2{\tan }^2\phi )}-\left\{\frac{(1+{\tan }^2\phi )}{[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}\right\}$
	$=$	$1-\frac{1}{Q^2}-\left\{\frac{1/{\sin }^2\phi }{[q^2{\lambda }_2{Q}^2-(q^2-1)]}\right\}=\frac{1}{Q^2[]}\{Q^2[]-[]-\frac{Q^2}{{\sin }^2\phi }\},$
$\frac{x^2+q^2{y}^2}{{\lambda }_1^2}$	$=$	$1-[1+\frac{q^2{\tan }^2\phi }{(1+q^2{\tan }^2\phi )}]\left\{\frac{(1+{\tan }^2\phi )}{[(1+q^2{\tan }^2\phi ){\lambda }_2-(q^2-1){\tan }^2\phi ]}\right\}.$

Now, notice that,

$\frac{q^2{y}^2{Q}^2}{{\lambda }_1^2}$

$=$

$1-\frac{1}{[]{\sin }^2\phi },$

and,

$\frac{x^2}{{\lambda }_1^2}+\frac{1}{Q^2}$

$=$

$1-\frac{1}{[]{\sin }^2\phi }.$

Hence,

$\frac{x^2}{{\lambda }_1^2}+\frac{1}{Q^2}$	$=$	$\frac{q^2{y}^2{Q}^2}{{\lambda }_1^2}$
$\Rightarrow 0$	$=$	$Q^4\left(\frac{q^2{y}^2}{{\lambda }_1^2}\right)-Q^2\left(\frac{x^2}{{\lambda }_1^2}\right)-1$
	$=$	$Q^4-Q^2\left(\frac{x^2}{q^2{y}^2}\right)-\left(\frac{{\lambda }_1^2}{q^2{y}^2}\right),$

where,

$Q^2$

$\equiv$

$\frac{1+q^2{\tan }^2\phi }{q^2{\tan }^2\phi }.$

Solving the quadratic equation, we have,

$Q^2$	$=$	$\frac{1}{2}\left\{\right(\frac{x^2}{q^2{y}^2})\pm [(\frac{x^2}{q^2{y}^2}{)}^2+4(\frac{{\lambda }_1^2}{q^2{y}^2}\left){]}^{1/2}\right\}$
	$=$	$\left(\frac{x^2}{2q^2{y}^2}\right)\{1\pm [1+4\left(\frac{{\lambda }_1^2{q}^2{y}^2}{x^4}\right){]}^{1/2}\}.$

Tentative Summary ${\lambda }_1$ $\equiv$ $(x^2+q^2{y}^2+p^2{z}^2{)}^{1/2},$ ${\lambda }_2$ $\equiv$ $\frac{(x^2+y^2{)}^{1/2}}{pz},$ ${\lambda }_3=Q^2$ $\equiv$ $\left(\frac{x^2}{2q^2{y}^2}\right)\{1\pm [1+4\left(\frac{{\lambda }_1^2{q}^2{y}^2}{x^4}\right){]}^{1/2}\}.$

Partial Derivatives & Scale Factors

First Coordinate

$\frac{\partial {\lambda }_1}{\partial x}$	$=$	$\frac{x}{{\lambda }_1},$
$\frac{\partial {\lambda }_1}{\partial y}$	$=$	$\frac{q^{2}y}{{\lambda }_1},$
$\frac{\partial {\lambda }_1}{\partial z}$	$=$	$\frac{p^{2}z}{{\lambda }_1}.$

$h_1^{-2}$	$=$	$(\frac{\partial {\lambda }_1}{\partial x}{)}^2+(\frac{\partial {\lambda }_1}{\partial y}{)}^2+(\frac{\partial {\lambda }_1}{\partial z}{)}^2$	$=$	$(\frac{x}{{\lambda }_1}{)}^2+(\frac{q^{2}y}{{\lambda }_1}{)}^2+(\frac{p^{2}z}{{\lambda }_1}{)}^2.$
$\Rightarrow h_1$	$=$	${\lambda }_1{\ell }_{3D},$

where,

${\ell }_{3D}\equiv (x^2+q^4{y}^2+p^4{z}^2{)}^{-1/2}.$

As a result, the associated unit vector is,

${\hat{e}}_1$	$=$	$\hat{ı}{h}_1\left(\frac{\partial {\lambda }_1}{\partial x}\right)+\hat{ȷ}{h}_1\left(\frac{\partial {\lambda }_1}{\partial y}\right)+\hat{k}{h}_1\left(\frac{\partial {\lambda }_1}{\partial z}\right)$
	$=$	$\hat{ı}x{\ell }_{3D}+\hat{ȷ}{q}^{2}y{\ell }_{3D}+\hat{k}{p}^{2}z{\ell }_{3D}.$

Notice that,

${\hat{e}}_1\cdot {\hat{e}}_1$

$=$

$(x^2+q^4{y}^2+p^4{z}^2){\ell }_{3D}^2=1.$

Second Coordinate (1^st Try)

$\frac{\partial {\lambda }_2}{\partial x}$	$=$	$\frac{1}{pz}\left[\frac{x}{(x^2+y^2{)}^{1/2}}\right],$
$\frac{\partial {\lambda }_2}{\partial y}$	$=$	$\frac{1}{pz}\left[\frac{y}{(x^2+y^2{)}^{1/2}}\right],$
$\frac{\partial {\lambda }_2}{\partial z}$	$=$	$-\frac{(x^2+y^2{)}^{1/2}}{p{z}^2}.$

$h_2^{-2}$	$=$	$(\frac{\partial {\lambda }_2}{\partial x}{)}^2+(\frac{\partial {\lambda }_2}{\partial y}{)}^2+(\frac{\partial {\lambda }_2}{\partial z}{)}^2$
	$=$	$\left\{\frac{1}{pz}\right[\frac{x}{(x^2+y^2{)}^{1/2}}]{\}}^2+\{\frac{1}{pz}\left[\frac{y}{(x^2+y^2{)}^{1/2}}\right]{\}}^2+\{\frac{(x^2+y^2{)}^{1/2}}{p{z}^2}{\}}^2$
	$=$	$\left\{\right[\frac{x^2}{(x^2+y^2)p^2{z}^2}\left]\right\}+\left\{\right[\frac{y^2}{(x^2+y^2)p^2{z}^2}\left]\right\}+\left\{\frac{(x^2+y^2)}{p^2{z}^4}\right\}$
	$=$	$\frac{1}{p^2{z}^2}+\frac{(x^2+y^2)}{p^2{z}^4}=\frac{(x^2+y^2+z^2)}{p^2{z}^4}$
$\Rightarrow h_2$	$=$	$\frac{p{z}^2}{r}$

As a result, the associated unit vector is,

${\hat{e}}_2$	$=$	$\hat{ı}{h}_2\left(\frac{\partial {\lambda }_2}{\partial x}\right)+\hat{ȷ}{h}_2\left(\frac{\partial {\lambda }_2}{\partial y}\right)+\hat{k}{h}_2\left(\frac{\partial {\lambda }_2}{\partial z}\right)$
	$=$	$\hat{ı}\left[\frac{xz}{r(x^2+y^2{)}^{1/2}}\right]+\hat{ȷ}\left[\frac{yz}{r(x^2+y^2{)}^{1/2}}\right]-\hat{k}\left[\frac{(x^2+y^2{)}^{1/2}}{r}\right].$

Notice that,

${\hat{e}}_2\cdot {\hat{e}}_2$

$=$

$\left[\frac{x^2{z}^2}{r^2(x^2+y^2)}\right]+\left[\frac{y^2{z}^2}{r^2(x^2+y^2)}\right]+\left[\frac{(x^2+y^2)}{r^2}\right]=1.$

Let's check to see if this "second" unit vector is orthogonal to the "first."

${\hat{e}}_1\cdot {\hat{e}}_2$	$=$	$x{\ell }_{3D}\left[\frac{xz}{r(x^2+y^2{)}^{1/2}}\right]+q^{2}y{\ell }_{3D}\left[\frac{yz}{r(x^2+y^2{)}^{1/2}}\right]-p^{2}z{\ell }_{3D}\left[\frac{(x^2+y^2{)}^{1/2}}{r}\right]$
	$=$	${\ell }_{3D}\left\{\right[\frac{x^{2}z}{r(x^2+y^2{)}^{1/2}}]+[\frac{q^2{y}^{2}z}{r(x^2+y^2{)}^{1/2}}]-[\frac{p^{2}z(x^2+y^2{)}^{1/2}}{r}\left]\right\}$
	$=$	$\frac{z{\ell }_{3D}}{r(x^2+y^2{)}^{1/2}}\left\{\right[x^2]+[q^2{y}^2]-[p^2(x^2+y^2)\left]\right\}$
	$\ne$	$0.$

Second Coordinate (2^nd Try)

Let's try,

${\lambda }_2$	$=$	$\left[\frac{(x^2+q^2{y}^2+\mathfrak{𝔣}\cdot p^2{z}^2{)}^{1/2}}{pz}\right],$
$\Rightarrow \frac{\partial {\lambda }_2}{\partial x}$	$=$	$\frac{x}{pz(x^2+q^2{y}^2+\mathfrak{𝔣}\cdot p^2{z}^2{)}^{1/2}}=\frac{x}{p^2{z}^2{\lambda }_2},$
$\frac{\partial {\lambda }_2}{\partial y}$	$=$	$\frac{q^{2}y}{pz(x^2+q^2{y}^2+\mathfrak{𝔣}\cdot p^2{z}^2{)}^{1/2}}=\frac{q^{2}y}{p^2{z}^2{\lambda }_2},$
$\frac{\partial {\lambda }_2}{\partial z}$	$=$	$\frac{\mathfrak{𝔣}\cdot p^{2}z}{pz(x^2+q^2{y}^2+\mathfrak{𝔣}\cdot p^2{z}^2{)}^{1/2}}-\frac{(x^2+q^2{y}^2+\mathfrak{𝔣}\cdot p^2{z}^2{)}^{1/2}}{p{z}^2}=\frac{1}{p^2{z}^2{\lambda }_2}(\mathfrak{𝔣}\cdot p^{2}z)-\frac{{\lambda }_2}{z}=\frac{1}{p^2{z}^2{\lambda }_2}(\mathfrak{𝔣}\cdot p^{2}z-p^{2}z{\lambda }_2^2).$

Hence,

$h_2^{-2}$	$=$	$(\frac{\partial {\lambda }_2}{\partial x}{)}^2+(\frac{\partial {\lambda }_2}{\partial y}{)}^2+(\frac{\partial {\lambda }_2}{\partial z}{)}^2$
	$=$	$[\frac{x}{p^2{z}^2{\lambda }_2}{]}^2+[\frac{q^{2}y}{p^2{z}^2{\lambda }_2}{]}^2+[\frac{\mathfrak{𝔣}}{z{\lambda }_2}-\frac{{\lambda }_2}{z}{]}^2$
	$=$	$\left[\frac{x^2+q^4{y}^2}{p^4{z}^4{\lambda }_2^2}\right]+\left[\frac{1}{z{\lambda }_2}\right(\mathfrak{𝔣}-{\lambda }_2^2){]}^2$
	$=$	$\frac{1}{p^4{z}^4{\lambda }_2^2}[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2]$
$\Rightarrow h_2$	$=$	$\frac{p^2{z}^2{\lambda }_2}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}.$

So, the associated unit vector is,

${\hat{e}}_2$	$=$	$\hat{ı}{h}_2\left(\frac{\partial {\lambda }_2}{\partial x}\right)+\hat{ȷ}{h}_2\left(\frac{\partial {\lambda }_2}{\partial y}\right)+\hat{k}{h}_2\left(\frac{\partial {\lambda }_2}{\partial z}\right)$
	$=$	$\hat{ı}\left\{\frac{x}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\right\}+\hat{ȷ}\left\{\frac{q^{2}y}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\right\}+\hat{k}\left\{\frac{p^{2}z(\mathfrak{𝔣}-{\lambda }_2^2)}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\right\}.$

Checking orthogonality …

${\hat{e}}_1\cdot {\hat{e}}_2$	$=$	$x{\ell }_{3D}\left\{\frac{x}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\right\}+q^{2}y{\ell }_{3D}\left\{\frac{q^{2}y}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\right\}+p^{2}z{\ell }_{3D}\left\{\frac{p^{2}z(\mathfrak{𝔣}-{\lambda }_2^2)}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\right\}$
	$=$	$\frac{{\ell }_{3D}}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\{x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2)\}.$
	$=$	$\frac{{\ell }_{3D}}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\{x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2)\}.$

If $\mathfrak{𝔣}=0$, we have …

$p^{2}z(\mathfrak{𝔣}-{\lambda }_2^2)$

$\to$

$[-p^{2}z{\lambda }_2^2{]}_{\mathfrak{𝔣}=0}=-p^{2}z[\frac{(x^2+q^2{y}^2+{\xcancel{\mathfrak{𝔣}\cdot }}^0{p}^2{z}^2{)}^{1/2}}{pz}{]}^2=-\frac{(x^2+q^2{y}^2)}{z},$

which, in turn, means …

$[x^2+q^4{y}^2+p^4{z}^2({\xcancel{\mathfrak{𝔣}}}^0-{\lambda }_2^2{)}^2{]}^{1/2}$	$=$	$[x^2+q^4{y}^2+p^4{z}^2{\lambda }_2^4{]}^{1/2}$
	$=$	$\{x^2+q^4{y}^2+p^4{z}^2[\frac{(x^2+q^2{y}^2+{\xcancel{\mathfrak{𝔣}\cdot }}^0{p}^2{z}^2{)}^{1/2}}{pz}{]}^4{\}}^{1/2}$
	$=$	$\{x^2+q^4{y}^2+[\frac{(x^2+q^2{y}^2{)}^2}{z^2}]{\}}^{1/2}$
	$=$	$(x^2+q^4{y}^2{)}^{1/2}[1+\frac{(x^2+q^2{y}^2)}{z^2}{]}^{1/2}$
	$=$	$\frac{(x^2+q^4{y}^2{)}^{1/2}}{z}[z^2+(x^2+q^2{y}^2){]}^{1/2},$

and,

${\hat{e}}_1\cdot {\hat{e}}_2$

$=$

$\frac{{\ell }_{3D}}{[x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2{)}^2{]}^{1/2}}\{x^2+q^4{y}^2+p^4{z}^2(\mathfrak{𝔣}-{\lambda }_2^2)\}.$