# [SOLVED]Mathematica acting strange

#### dwsmith

##### Well-known member
Can someone identity what the issue here is before I throw my computer out the window.
By the way, this just worked 10mins ago. I restarted Mathematica and my computer but it now insist z isn't an equation.
Code:
ClearAll["Global*"];
me = 5.974*10^(24);
mm = 7.348*10^(22);
G = 6.67259*10^(-20);
\[Mu] = G*(me + mm);
re = 6378;
rm = 1737;
\[Pi]1 = me/(me + mm);
\[Pi]2 = mm/(me + mm);
x = -4671;
y = -6578;
r12 = r1 = r2 = 384400;
(*r1=Sqrt[(x+\[Pi]2*r12)^2+y^2];
r2=Sqrt[(x-\[Pi]1*r12)^2+y^2];*)
M = me + mm; vi = 8;
\[Nu] = -\[Pi]/2;
e = 1;
vi = 10.8662;

\[Gamma] = ArcTan[e*Sin[\[Nu]]/(1 + e*Cos[\[Nu]])];
vx = vi*(Sin[\[Gamma]]*Cos[\[Nu]] - Cos[\[Gamma]]*Sin[\[Nu]]);
vy = vi*(Sin[\[Gamma]]*Sin[\[Nu]] + Cos[\[Gamma]]*Cos[\[Nu]]);
rx = -4671;
ry = -6578;
rz = 0;

\[CapitalOmega] = Sqrt[\[Mu]/r12^3];
\[Mu]1 = G*me;
\[Mu]2 = G*mm;

r0 = {rx, ry, rz};
v0 = {vx, vy, rz};

s = NDSolve[{x''[t] -
2*\[CapitalOmega]*y'[t] - \[CapitalOmega]^2*
x[t] == -\[Mu]1/r1^3*(x[t] + \[Pi]2*r12) - \[Mu]2/
r2^3*(x[t] - \[Pi]1*r12),
y''[t] -
2*\[CapitalOmega]*x'[t] - \[CapitalOmega]^2*
y[t] == -\[Mu]1/r1^3*y[t] - \[Mu]2/r2^3*y[t],
z''[t] == -\[Mu]1/r1^3*z[t] - \[Mu]2/r2^3*z[t],
x == r0[],
y == r0[],
z == r0[],
x' == v0[],
y' == v0[],
z' == v0[]},
{x, y, z}, {t, 0, 1000000}];

NDSolve::deqn: Equation or list of equations expected instead of False in the first argument {0. -7.10426\[CenterDot]10^-12 (-4671)[t]==-8.63204\[CenterDot]10^-14 (-379729.+(-4671)[t])-7.01794\[CenterDot]10^-12 (4670.66 +(-4671)[t]),0. -7.10426\[CenterDot]10^-12 (-6578)[t]==-7.10426\[CenterDot]10^-12 (-6578)[t],<<5>>,False,(z^\[Prime])==0}. >>`

#### MarkFL

Staff member
...before I throw my computer out the window...
Sorry, can't help with the Mathematica issue, but just wanted to say I have considered throwing my computer in my pond before. #### Ackbach

##### Indicium Physicus
Staff member
You define

x = -4671;
y = -6578;

and then you use both x = x[t] and y = y[t] in NDSolve. That might be tripping you up. Try renaming variables. What might especially confirm this is that the double equals, which is definitely what you need in NDSolve, will yield TRUE or FALSE if the stuff on either side is already defined.

When something works, and then it doesn't work, in Mathematica, that's typically happening because of the order in which cells are evaluated. If these commands are spread out over a bunch of different cells, then the order really matters.

#### dwsmith

##### Well-known member
You define

x = -4671;
y = -6578;

and then you use both x = x[t] and y = y[t] in NDSolve. That might be tripping you up. Try renaming variables. What might especially confirm this is that the double equals, which is definitely what you need in NDSolve, will yield TRUE or FALSE if the stuff on either side is already defined.

When something works, and then it doesn't work, in Mathematica, that's typically happening because of the order in which cells are evaluated. If these commands are spread out over a bunch of different cells, then the order really matters.
The only problem was mathematica. I copied everything over to a new notebook and it worked.

#### Ackbach

##### Indicium Physicus
Staff member
The only problem was mathematica. I copied everything over to a new notebook and it worked.
Yep, that's a good trick, too. Glad it's working for you now.