Question:

Sum of operations involving an arbitrary number of 2D vectors

Aubrey: 2 days ago

I need to define an equation stating that the sum of n operations involving n 2D vectors and n scalars yields zero, where n is an arbitrary integer greater than 1.

For example, think of it as Sum[(v_i + t)*(Norm[v_i+t]-L_i), {i, 1, n}] == 0 where v_i are the n 2D vectors, t is the unknown (which is also a 2D vector), and L_i are the n scalars.

How should I define the v_i vectors and the L_i scalars so that I can best index them from the sum operator? Note that the Norm[] operator is used, so Mathematica needs to know vectors are 2D, and that scalars are scalars (i.e. I just cannot define the equation like if all variables were scalars and understand them as vectors in an abstract way).

Answer:

Kai: 2 days ago

Your unknowns

t = {tx, ty}

Assuming you have already defined your v and L on your own, here I provide some random values for them

Option 1

ClearAll[v, L]
Do[v[i] = RandomReal[1, 2], {i, 7}]
Do[L[i] = RandomReal[1], {i, 7}]

your equation

Sum[(v[i] + t)*(Norm[v[i] + t] - L[i]), {i, 1, 7}] == 0

Option 2

ClearAll[v, L]
v = RandomReal[1, {7, 2}]
L = v = RandomReal[1, {7, 2}]
Sum[(v[[i]] + t)*(Norm[v[[i]] + t] - L[[i]]), {i, 1, 7}] == 0

Notice the difference in the definitions for v and L use of down values or own values in the two options. See here (https://mathematica.stackexchange.com/q/96/10397).

Is that what you need?