## 173 Reputation

15 years, 126 days

## Thanks...

Robert, Thanks, and my apologies to ichyfat and Acer for the misleading post above. It occurs to me that graph is the same in either case I stated above. This is simply more evidence that the we just can't get by without mathematicians:) Thomas

## more...

Here are the others For y=0, set x = t and then from the equation 3x^2-z=0 we get z = 3*t^2 spc1:=spacecurve([t,0,3*t^2], t=-2..2, thickness=2, color=green): For x = 0, set y = t and then from the equation 5y^2+z=0 we get z = -5*t^2 spc2:=spacecurve([0,t,-5*t^2], t=-2..2, thickness=2, color=blue): Here is the whole thing: restart: with(plots): S:=[solve(3*t^2-5*y^2=0,y)]; p1:=plot3d(3*x^2-5*y^2, x=-2..2, y=-2..2): spc:=spacecurve({[t, S, 0],[t,S,0]}, t=-2..2, thickness=2, color=red): spc1:=spacecurve([t,0,3*t^2], t=-2..2, thickness=2, color=green): spc2:=spacecurve([0,t,-5*t^2], t=-2..2, thickness=2, color=blue): display([p1,spc,spc1,spc2]);

## more...

Here are the others For y=0, set x = t and then from the equation 3x^2-z=0 we get z = 3*t^2 spc1:=spacecurve([t,0,3*t^2], t=-2..2, thickness=2, color=green): For x = 0, set y = t and then from the equation 5y^2+z=0 we get z = -5*t^2 spc2:=spacecurve([0,t,-5*t^2], t=-2..2, thickness=2, color=blue): Here is the whole thing: restart: with(plots): S:=[solve(3*t^2-5*y^2=0,y)]; p1:=plot3d(3*x^2-5*y^2, x=-2..2, y=-2..2): spc:=spacecurve({[t, S, 0],[t,S,0]}, t=-2..2, thickness=2, color=red): spc1:=spacecurve([t,0,3*t^2], t=-2..2, thickness=2, color=green): spc2:=spacecurve([0,t,-5*t^2], t=-2..2, thickness=2, color=blue): display([p1,spc,spc1,spc2]);

## plot...

I am not sure why the plots are not showing above. I tried to edit it without success.

## plot...

I am not sure why the plots are not showing above. I tried to edit it without success.

## changecoords...

Thanks DJ, I had looked at this, but it seems to work only for expressions and Jerry had asked how to convert the coordinates of a point. restart: changecoords([1,1,0],[x,y,z],spherical,[r,theta,phi]); [1, 1, 0] Also, I think it only goes from Cartesian to other. Additionally, in regard to what J. Tarr had referred to, the convention here is to give spherical coordinates ordered [r, theta, phi] as opposed to [r, phi, theta] in VectorCalculus. It appears that phi is still measured from the positive z-axis in this case. changecoords(x,[x,y,z],spherical,[r,theta,phi]); r sin(phi) cos(theta) changecoords(y,[x,y,z],spherical,[r,theta,phi]); r sin(phi) sin(theta) changecoords(z,[x,y,z],spherical,[r,theta,phi]); r cos(phi)

## changecoords...

Thanks DJ, I had looked at this, but it seems to work only for expressions and Jerry had asked how to convert the coordinates of a point. restart: changecoords([1,1,0],[x,y,z],spherical,[r,theta,phi]); [1, 1, 0] Also, I think it only goes from Cartesian to other. Additionally, in regard to what J. Tarr had referred to, the convention here is to give spherical coordinates ordered [r, theta, phi] as opposed to [r, phi, theta] in VectorCalculus. It appears that phi is still measured from the positive z-axis in this case. changecoords(x,[x,y,z],spherical,[r,theta,phi]); r sin(phi) cos(theta) changecoords(y,[x,y,z],spherical,[r,theta,phi]); r sin(phi) sin(theta) changecoords(z,[x,y,z],spherical,[r,theta,phi]); r cos(phi)

## Thanks...

Thanks, Georgios. It does seem odd, especially since "convert" works in the limited cases above. I'm not complaining though, since I love the way VectorCalculus displays vectors in terms of basis vectors.

## Thanks...

Thanks, Georgios. It does seem odd, especially since "convert" works in the limited cases above. I'm not complaining though, since I love the way VectorCalculus displays vectors in terms of basis vectors.

## convert...

Yes, thanks Georgios, that is what I was using as an example of a simple method. But, if you look at the OP, Jerry wanted to convert between cartesian ,spherical and cylindrical and I don't think "convert" can do this. If it can I am not sure how to enter the information.

## convert...

Yes, thanks Georgios, that is what I was using as an example of a simple method. But, if you look at the OP, Jerry wanted to convert between cartesian ,spherical and cylindrical and I don't think "convert" can do this. If it can I am not sure how to enter the information.

## convenience...

I think it's just a convenience, and sort of a nice one, since is saves you having to write the parameterization explicitly. Up until today I never looked at the coords option in plot3d. I just defined my own parameterization explicitly as you suggest. However, plot3d(1,theta=0..2*Pi,phi=0..Pi/2,coords=spherical,axes=boxed,scaling=constrained); is kind of a nice way to get a quick plot of a hemisphere.

## convenience...

I think it's just a convenience, and sort of a nice one, since is saves you having to write the parameterization explicitly. Up until today I never looked at the coords option in plot3d. I just defined my own parameterization explicitly as you suggest. However, plot3d(1,theta=0..2*Pi,phi=0..Pi/2,coords=spherical,axes=boxed,scaling=constrained); is kind of a nice way to get a quick plot of a hemisphere.