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2015-03-26 22:10:10 -0500 marked best answer Solving linear matrix equations

Hi everybody, I'm new to Sage and I'm pretty confused with the solving of matrix equations, I didn't fully understand the guide.

I've got these vectors:

V_fa = vector([V_f*cos(phi), V_f*sin(phi), 0])

V_ra = vector([V, 0, 0])

omega = vector([0, 0, L*psi_d])

P = vector([0, L*psi_d, 0])

And i want to implement the equation:

V_fa=V_ra+omega.cross_product(P)

to isolate and obtain the value of psi_d.

How can I do that?

Thank you very much

2015-01-14 03:41:20 -0500 commented answer Transpose of a column vector

Thank you for your reply. May I ask you what is the difference between a list and a vector?

2015-01-12 16:17:55 -0500 received badge  Commentator
2015-01-12 16:17:55 -0500 commented answer Transpose of a column vector
  1. I need to transpose the vector because when i use it in a sum it says unsupported operand parent(s) for '+': 'Full MatrixSpace of 3 by 1 dense matrices over Symbolic Ring' and 'Vector space of dimension 3 over Symbolic Ring' , so i thought maybe it was because it had to be a row vector.

    1. Why if i do v.row() it still says row() takes at least 1 positional argument (0 given) ?
2015-01-12 12:04:10 -0500 asked a question Transpose of a column vector

Hi, I've got a column vector and I need to transpose it. But when i do: v=v.column() it says column() takes at least 1 positional argument (0 given)

I've also tried doing v=Matrix([[1, 0, 0],[0, 1, 0], [0, 0, 1],])*v.column() which worked before but still doesn't work.

What is the problem here?

Thank you

2015-01-12 06:57:17 -0500 commented answer Derivative of a function

Thank you so much!!

2015-01-12 05:52:24 -0500 asked a question Derivative of a function

Hi, I've got this two functions:

psi=function('psi',t)
psi_d=function('psi_d',t)
psi=(sin(delta(t))*v(t))/(l*cos(delta(t)))
psi_d=diff(psi)

but it says No differentiation variable specified how can I derivate psi? Please someone help me it's driving me crazy since yesterday!

Thank you very much

2015-01-11 15:34:34 -0500 commented answer Equations solving

Now the problem is that when i do solve(eqq1,diff(psi(t))) he doesn't solve it (it gives me [ ]), and if i do solve(eqq1,diff(psi)) is says No differentiation variable specified.

What's wrong?

2015-01-11 15:29:02 -0500 commented answer Equations solving

Ok i got it, i just had to writeeqq1=eqq1.subs(V_f==V_ff)

2015-01-11 15:25:55 -0500 commented answer Equations solving

I redefined eqq1, but doing like this it ignores the left part of the equation, so eqq1 becomes just sin(delta(t))*v/cos(delta(t))

2015-01-11 14:27:36 -0500 commented answer Equations solving

It works! Grazie mille! ;)

Now i substituted that value in the second equation doing eqq1.left().subs(V_f==V_ff)

but when i do

solve(eqq1,diff(psi))

it gives me diff(psi(t))=V_f*sin(delta(t))/l

like i never did that substitution before.

What can i do to have diff(psi(t))=[v(t)*tan(delta(t))]/l as a solution?

2015-01-11 13:16:36 -0500 asked a question Equations solving

Hi everybody, i've got this two equations:

eqq0: V_f*cos(delta(t))=v(t)
eqq1: V_f*sin(delta(t))=l*diff(psi(t))

I need to isolate V_f from the first equation, obtaining V_f=v(t)/cos(delta(t)) and substitute it in the second equation. Then i have to isolate diff(psi(t))=[v(t)*tan(delta(t))]/l.

I did :

a=solve (eqq0,V_f)
V_ff=a.right()

but it says "AttributeError: 'Sequence_generic' object has no attribute 'right'"

How can i solve this two equations?

Thank you.

2014-12-23 03:49:24 -0500 edited question Sum of two vectors

Hi everybody, i've got this functions and variables:

v = function('v',t)
a_V_ra = function('a_V_ra',t)
a_a_ra=function('a_a_ra',t) 
g = var('g')

r_V_ra = vector([v,0,0])
a_V_ra = R_ra*r_V_ra.column()

where R is a matrix and a_V_ra is the vector [cos(psi(t))v(t), sin(psi(t))v(t),0].

But when i do this:

a_a_ra = diff(a_V_ra)+vector([0,0,-g])

it says: TypeError: unsupported operand parent(s) for '+': 'Full MatrixSpace of 3 by 1 dense matrices over Symbolic Ring' and 'Vector space of dimension 3 over Symbolic Ring'

I guess it's saying that i'm summing a matrix and a vector, but they're both vectors! What can I do to make it work?

Thank you.

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