MaplePrimes - answers and comments on Question, Generating list of equations to solve

hard to see

Joe Riel — Thu, 15 Dec 2011 20:51:17 Z

I'm having a hard time reading the Maple code, the font displays badly on my machine. It appears that you wrote

col := seq(fn_i = ... , i = 1..9);

You probably want to change that to

col = seq(fn[i] = ... i=1..9);

Just to confuse the matter, they could be equivalent, since typing underscore in 2D match is equivalent to using square brackets, however, if you had done that I wouldn't expect to *see* the underscore in the text, it would have expanded to a subscript.

catenation and solve

Joe Riel — Fri, 16 Dec 2011 01:04:37 Z

Could be, I'm also using linux.

There are two problems. Because you are using actual underscores (rather than indices) for the names, you cannot use

seq( ... fp_i ... , i = 1..9)

to reference the fp_x variables. You can fix that by using the catenate operator, ||

col := seq(fn_||i = (1-1/tau)*fp_||i + 1/tau * feq(i), i = 1..9):

The second problem is that while you have 10 equations, you only give solve 7 variables. You need to specify more variables. For example

eqs := { massconserv, col };
vars := { seq(fp_||i, i=1..9), rho_wall }:
solve(eqs, vars);

In maple i'm using 2D input so fn_i is being

kieranhood — Thu, 15 Dec 2011 22:32:08 Z

In maple i'm using 2D input so fn_i is being evaluated as a index, so I don't think that's the problem. Is seq the correct command to generate a system of equations like this?

The text looks a little weird to me aswell, I thought it was just because I was using linux. Here's it in normal text:

rho_in := fp_5 + fp_7 + fp_8

rho_out := fn_4 + fn_6 + fn_9

massconserv := rho_in = rho_out

w:= [ 4/9, 1/9, 1/9, 1/9, 1/9, 1/36, 1/36, 1/36, 1/36 ]

feq := i-> rho_wall * w[i]

col := seq(fn_i = (1-1/tau)*fp_i + 1/tau * feq(i), i = 1..9)

solve( { massconserv, col }, { fp_4, fp_5, fp_6, fp_7, fp_8, fp_9, rho_wall } )