Urgent Help Needed For Python

[shakshakshuk]

Hi everyone,

I have recently been introduced to python in my university and now I have an assignment to submit.
My problem is that I don't have much python programming experience.

I was asked to write a program to:
1. Enter coefficients
2. check solvability
3. Do gauss seidel
4. Do gauss jacobi

I have started writing my "simple" program when I encountered an error which I can't debug. Here are my latest codings:

def menu():
    print"(1) Enter coefficients"
    print"(2) Check solvability"
    print"(3) Gauss-Seidel"
    print"(4) Gauss-Jacobi"

    choice=input("Your choice is:")
    if 1<=choice<=4:
        if choice==1:
            coeff()
        if choice==2:
            check()
    else:
        print
        print"ERROR! Either wrong number chosen or letters have been entered."
        print"Please choose a number from 1 to 4 only."
        print
        
def coeff():
    try:
        global a1
        global b1
        global c1
        global a2
        global b2
        global c2
        global a3
        global b3
        global c3
        global d1
        global d2
        global d3
                
        a1=input("a1=")
        b1=input("b1=")
        c1=input("c1=")
        a2=input("a2=")
        b2=input("b2=")
        c2=input("c2=")
        a3=input("a3=")
        b3=input("b3=")
        c3=input("c3=")
        d1=input("d1=")
        d2=input("d2=")
        d3=input("d3=")
        print
    except:
        print
        print"Error occured! Please check and re-enter your values."
        coeff()
        print
        
def check():
    if a1<0:
        a1=-a1
    if b1<0:
        b1=-b1
    if c1<0:
        c1=-c1
    if a2<0:
        a2=-a2
    if b2<0:
        b2=-b2
    if c2<0:
        c2=-c2
    if a3<0:
        a3=-a3
    if b3<0:
        b3=-b3
    if c3<0:
        c3=-c3

    if a1>b1+c1:
        if b2>a2+c2:
            if c3>a3+b3:
                print"This system of linear equations can be solved using Gauss-Jacobi and Gauss-Seidel."
            else:
                print"This system of linear equations cannot be solved using Gauss-Jacobi and Gauss-Seidel."
        


while True:
    menu()

I haven't done the part on gauss seidel and gauss jacobi. But concerning the second choice in my menu, it returns the :
"UnboundLocalEr ror: local variable 'a1' referenced before assignment"

I really don't know what to do and I have only 2 weeks to submit my assignment. Your assistance will be of a great help.

Thank you in advance for the help you have provided to me and please excuse me if my english was not good.

[Laharl]

First, please use CODE tags when posting your code. This is especially important with Python because the forum parser strips out all that syntactic whitespace.

The reason that it's complaining about a1 is that a1 isn't declared anywhere. It'd complain about any of your other global variables for the same reason. Just because you say you want to use a global variable in a function, it doesn't follow that the global variable exists. If you want to do it with a global, then somewhere in global scope, you need to declare that. I would assume you should initialize it to 0.

[labmonkey111]

You need the global declarations in all of you functions. Python assumes all variables are local unless you explicitly say otherwise.

[shakshakshuk]

You need the global declarations in all of you functions. Python assumes all variables are local unless you explicitly say otherwise.

Thank you again for your help. Declaring the global variables in each function, including my main program was a great idea. It finally works.
All I need to do now is to calculate gauss seidel and gauss jacobi.

I have quite a good idea how to do the gauss seidel, but I am having problems using gauss jacobi as whenever the value of x1 has been calculated, it replaces it in my next equation, like in gauss seidel.

x1=(d1-b1y0-c1z0)/a1
y1=(d2-a2x1-c2z0)/b2
z1=(d3-a3x1-b3y1)/c3

This is one line for my code for gauss seidel. It works perfectly. The problem is with gauss jacobi. The x1 in the second and third equation should be x0 and y1 in the third equation should be y0. But when I change these to x0 and y0, my loop fails to work.

[labmonkey111]

What are the terms you have like this: b1y0?

Is 'b1y0' a variable name? Or do you mean it to be multiplication? Like b1*y0?

[shakshakshuk]

What are the terms you have like this: b1y0?

Is 'b1y0' a variable name? Or do you mean it to be multiplication? Like b1*y0?

I am really very sorry for this error. What I meant was b1*y0.
Sorry about this mistake again. The fact was that I had to work till late on my second assignment and I was feeling a bit sleepy when I posted my request