# NDSolve problem: Power::infy: Infinite expression 1/0. encountered

I am trying to solve system of 15 differential equations:

eqdiffu1 =
{D[yu, t] == bu, D[yd, t] == bd,
D[yl, t] == yl*(-sumg3[t] + 3yd.yd + 4 yl.yl),
D[vckm, t] == -ConjugateTranspose[elu].vckm +  vckm.eld,
(vckm /. {t -> 0}) == vckm1,
yu1 == yg2, yu2 == ys2, yu3[ttop] == yt2,  yd1 == ydo2,  yd2 == yc2,
yd3 == yb2, yl1 == yel2, yl2 == ym2, yl3 == ytau2};


with

sol =
NDSolve[
eqdiffu,
{v11[t], v12[t], v13[t],
v21[t], v22[t], v23[t],
v31[t], v32[t], v33[t],
yu1[t], yu2[t], yu3[t] ,
yd1[t], yd2[t], yd3[t],
yl1[t], yl2[t], yl3[t]},
{t, 0, 0.21}];


where yu, yd, yl are vectors and vckm and elu are matrices.

Mathematica produces the error messages:

Power::infy: Infinite expression 1/0. encountered.
Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered.
Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered.
Power::infy: Infinite expression 1/0. encountered.
General::stop: Further output of Power::infy will be suppressed during this calculation.
NDSolve::ndnum: Encountered non-numerical value for a derivative at t == 0..

I am sure there are no infinities in a denominator. Do you know where there could be a mistake?

• Maria, (1) you formulated the system entitled eqdiffu1, while you then solve eqdiffu. This may be an error. (2) As soon as yd.yd is supposed to be a dot product, that means that yd (and also yl) are supposed to be vectors. Mma, however, does not know that. A good idea would be to either write equations separately for each component, or to inform Mma about their vector origin. The latter may be done by starting the code with making a definition, like yd[t_]:={yd1[t], yd2[t]}. This is in the case of a 2D vector yd[t]`. Analogously you may try in a more complex case. – Alexei Boulbitch Jul 10 '18 at 11:58