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Sum of two vectors

asked 2014-12-23 03:42:05 -0500

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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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answered 2014-12-23 12:15:17 -0500

calc314 gravatar image

The problem is that diff(a_V_ra,t) is giving you a column vector and vector([0,0,-g]) is giving you a row vector. Further, Sage sees the first as a matrix and the second as a vector. You can fix this using .column() as you did earlier in your code.

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

gives:

[ cos(psi)*D[0](v)(t)]
[-sin(psi)*D[0](v)(t)]
[                  -g]

My full code is:

var('psi t g')
v = function('v',t)

R_ra=matrix([[cos(psi),sin(psi),0],[-sin(psi),cos(psi),0],[0,0,1]])

r_V_ra = vector([v,0,0])
a_V_ra = R_ra*r_V_ra.column()
a_a_ra = diff(a_V_ra,t)+vector([0,0,-g]).column()
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answered 2014-12-23 08:17:08 -0500

FrédéricC gravatar image

Maybe you can try something like that:

sage: m=matrix([[1],[0],[0]])
sage: v=vector([0,5,6])
sage: m.column(0)+v
(1, 5, 6)
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Asked: 2014-12-23 03:42:05 -0500

Seen: 121 times

Last updated: Dec 23 '14