User Portlet
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| Any help how to solve a couple of ODEs to get the variables a[t] and x[t] ? ode1= -1/2* x’[t]^2 == a’’[t] / a[t] + a’[t] /a[t]^2 And: ode2 = x’’[t] + 3 (a’ [t]/ a[t] ) x’[t] + v[t] ==0 where v[t] = v0 ( 1 - Exp [ - Sqrt... |
| I try to write MA code to define a new modified Einstein tensor: $ G'_{\mu\nu} = G_{\mu\nu}- \frac{1}{3} \left[ \left( \frac{1}{4} R^2 + \nabla_\sigma \nabla^\sigma R \right) g_{\mu\nu} + R R_{\mu\nu} - \nabla_\mu \nabla_\nu R \right], $ ... |
| Hello, I try to solve this system of 2nd order differential equations in variables $x(t,k),y(t,k)$ and $z(t,k)$ $k^2y + 3 H \dot{y} = \frac{1}{2z_0} ( H \dot{z} - \dot{z} ) + \frac{\dot{z}_0}{2z_0} ( 2 H z + \dot{z} ), ~~~~~~~~ (1)$ $H x... |
| I have this ODE equation: $\frac{1}{3\phi } \left( \frac{\dot{a}\dot{\phi} }{a} + \ddot{\phi} \right) + 2 \frac{\ddot{a}}{a} = \partial_i \partial_j \phi$ Where $ \phi(x,t) = \frac{1}{4} e^{k(t-x)} - \frac{1}{4} e^{-k(t-x)} $ Can... |
| Dear Wolfram team: I try to calculate : $T_{ab} = g_{ab} F_{gd} F^{gd} - F_a^g F_{bg}$, where $F_{ab} = \partial_a A_b - \partial_b A_a$, So I define $F_{ab}$ by: s[a_, b_] := D[v[b], a] - D[v[a], b] But how to define... |
| I'm facing an issue with the integral attached in the MA file. Can Mathematica establish this integral with large integration initial limit (a =- 10^9) ? In the current MA file, the integration only works because I set the initial integration... |