How to solve a system of FDE?

Question

Here is the system I am trying to solve

x = 1;

eqns = {x^((a - 1))*CaputoD[w[y, t], {t, a}] - D[w[y, t], y] == 
    D[w[y, t], {y, 2}] - D[w[y, t], {y, 4}] - w[y, t] - T[y, t] - 
     P[y, t] + 
     1, (x^((a - 1))*CaputoD[T[y, t], {t, a}] - 
      D[T[y, t], y]) == (1 + (T[y, t] + 1)^3)*D[T[y, t], {y, 2}] + 
     3*(T[y, t] + 1)^2*
      D[T[y, t], y]^2 + (D[w[y, t], y]^2 + D[w[y, t], {y, 2}]^2 + 
       w[y, t]^2) + D[T[y, t], y]*D[P[y, t], y] + 
     D[T[y, t], y]^2, (x^((a - 1))*CaputoD[P[y, t], {t, a}] - 
      D[P[y, t], y]) == D[P[y, t], {y, 2}] + D[T[y, t], {y, 2}]};

ics = {w[y, 0] == 0, T[y, 0] == 1, P[y, 0] == 0};

bcs = {{w[0, t] == 0, Derivative[2, 0][w][0, t] == 0, T[0, t] == 0, 
    P[0, t] == 1}, {w[1, t] == 0, Derivative[2, 0][w][1, t] == 0, 
    T[1, t] == 1, P[1, t] == 0}};

sol = NDSolveValue[{eqns, ics, bcs}, {w, T, P}, {y, 0, 1}, {t, 0, 10},
   Method -> {"FractionalStep", "DifferentiationOrder" -> a}]

NDSolveValue::bdmtd: The value of the option Method -> {FractionalStep,DifferentiationOrder->a} is not a known built-in method, a symbol that could be a user-defined method, or a list with a name followed by method options.

Note: I used these {FractionalStep,DifferentiationOrder->a} myself to see whether its available or not. I was checking the capability of NDSolve.

Is there a way to solve this system? Thanks

@ΑλέξανδροςΖεγγ "Fractional Differential Equation" — Nasser, Commented Jan 16, 2023 at 6:10
@zhk What problem do you try to solve? This system has different type for $0< \alpha \le 1$ - parabolic type, and for $1 <\alpha \le 2$ - hyperbolic type. In the last case you need to add initial data for derivatives as well. — Alex Trounev, Commented Jan 21, 2023 at 3:44
@zhk Please, note, that ics and bcs are inconsistent. Could we make some transition step to compute solution? — Alex Trounev, Commented Jan 23, 2023 at 5:01

Alex Trounev · Accepted Answer · 2023-10-24 09:46:30Z

This problem can be solved with using the Euler wavelets collocation method to discretized system of PDEs on y and predictor-corrector method to solve the system of FDEs in time. As a test for these methods we use numerical solution to the next problem

x = 1; eqns = {x^((a - 1))*CaputoD[w[y, t], {t, a}] - D[w[y, t], y] ==
    D[w[y, t], {y, 2}] - D[w[y, t], {y, 4}] - w[y, t] - T[y, t] - 
    P[y, t] + 
    1, (x^((a - 1))*CaputoD[T[y, t], {t, a}] - 
     D[T[y, t], y]) == (1 + (T[y, t] + 1)^3)*D[T[y, t], {y, 2}] + 
    3*(T[y, t] + 1)^2*
     D[T[y, t], y]^2 + (D[w[y, t], y]^2 + D[w[y, t], {y, 2}]^2 + 
      w[y, t]^2) + D[T[y, t], y]*D[P[y, t], y] + 
    D[T[y, t], y]^2, (x^((a - 1))*CaputoD[P[y, t], {t, a}] - 
     D[P[y, t], y]) == D[P[y, t], {y, 2}] + D[T[y, t], {y, 2}]};
ics = {w[y, 0] == 0, T[y, 0] == 1, P[y, 0] == 0};
bcs = {w[0, t] == 0, Derivative[2, 0][w][0, t] == 0, 
  T[0, t] == Exp[-100 t], P[0, t] == 1 - Exp[-100 t], w[1, t] == 0, 
  Derivative[2, 0][w][1, t] == 0, T[1, t] == 1, P[1, t] == 0};  var = {w, T, P};sol1 = 
 NDSolveValue[{eqns, ics, bcs} /. a -> 1, var, {y, 0, 1}, {t, 0,
    10}];

Visualization

Table[Plot3D[sol1[[i]][y, t], {y, 0, 1}, {t, 0, 1}, 
  ColorFunction -> Hue, AxesLabel -> Automatic, 
  PlotLabel -> var[[i]]], {i, 3}]

Note, that picture above is a solution of the original problem at a=1. We added some transition zone of about $t=10^{-2}$ to force NDSolve. We also can solve this problem with using the Euler wavelets colocation method as follows

UE[m_, t_] := EulerE[m, t];
psi[k_, n_, m_, t_] := 
  Piecewise[{{2^(k/2) UE[m, 2^k t - 2 n + 1], (n - 1)/2^(k - 1) <= t <
       n/2^(k - 1)}, {0, True}}];
PsiE[k_, M_, t_] := 
 Flatten[Table[psi[k, n, m, t], {n, 1, 2^(k - 1)}, {m, 0, M - 1}]]
k0 = 2; M0 = 4; With[{k = k0, M = M0}, 
 nn = Length[Flatten[Table[1, {n, 1, 2^(k - 1)}, {m, 0, M - 1}]]]];
dx = 1/(nn); xl = Table[l*dx, {l, 0, nn}]; ycol = 
 Table[(xl[[l - 1]] + xl[[l]])/2, {l, 2, 
   nn + 1}]; tcol = ycol; Psijk = 
 With[{k = k0, M = M0}, PsiE[k, M, t1]]; Int1 = 
 With[{k = k0, M = M0}, Integrate[PsiE[k, M, t1], t1]];
Int2 = Integrate[Int1, t1]; Int3 = Integrate[Int2, t1]; Int4 = 
 Integrate[Int3, t1];
Psi[y_] := Psijk /. t1 -> y; int1[y_] := Int1 /. t1 -> y;
int2[y_] := Int2 /. t1 -> y; int3[y_] := Int3 /. t1 -> y;
int4[y_] := Int4 /. t1 -> y;
wA = Table[wa[i][t], {i, nn}]; wB = Table[wb[i][t], {i, 4}];
w4[y_] := wA . Psi[y]; w3[y_] := wA . int1[y] + wB[[1]] ; 
w2[y_] := wA . int2[y] + wB[[1]] y + wB[[2]] ; 
w1[y_] := wA . int3[y] + wB[[1]] y^2/2 + wB[[2]] y + wB[[3]]; 
w0[y_] := 
 wA . int4[y] + wB[[1]] y^3/6 + wB[[2]] y^2/2 + wB[[3]] y + wB[[4]];
tA = Table[ta[i][t], {i, nn}]; tB = Table[tb[i][t], {i, 2}];
T2[y_] := tA . Psi[y]; T1[y_] := tA . int1[y] + tB[[1]] ; 
T0[y_] := tA . int2[y] + tB[[1]] y + tB[[2]] ; pA = 
 Table[pa[i][t], {i, nn}]; pB = Table[pb[i][t], {i, 2}];
P2[y_] := pA . Psi[y]; P1[y_] := pA . int1[y] + pB[[1]] ; 
P0[y_] := pA . int2[y] + pB[[1]] y + pB[[2]] ;
eqw = With[{w = w0[y], T = T0[y], 
    P = P0[y]}, (D[w, t] == 
     D[w, y] + D[w, {y, 2}] - D[w, {y, 4}] - w - T - P + 1)];
eqnw = Table[eqw, {y, ycol}];
eqT = With[{w = w0[y], T = T0[y], P = P0[y]}, 
   D[T, t] == (D[T, y] + (1 + (T + 1)^3)*D[T, {y, 2}] + 
      3*(T + 1)^2*D[T, y]^2 + (D[w, y]^2 + D[w, {y, 2}]^2 + w^2) + 
      D[T, y]*D[P, y] + D[T, y]^2)];
eqnT = Table[eqT, {y, ycol}];
eqP = With[{w = w0[y], T = T0[y], P = P0[y]}, 
  D[P, t] == (D[P, y] + D[P, {y, 2}] + D[T, {y, 2}])]; eqnP = 
 Table[eqP, {y, ycol}]; eqs = Join[eqnw, eqnT, eqnP];
(*ic=With[{w=wvec.Psi[0],T=Tvec.Psi[0],P=Pvec.Psi[0]},{w==0,T==1,P==0}\
];*)
bc = With[{w = w0[y], T = T0[y], P = P0[y]}, 
   Join[{w == 0, D[w, y, y] == 0, T == 0, P == 1} /. 
     y -> 0, {w == 0, D[w, y, y] == 0, T == 1, P == 0} /. y -> 1]];
icy = With[{w = w0[y], T = T0[y], 
   P = P0[y]}, {w == 0, T == 1, P == 0} /. t -> 0]; ic = 
 Table[icy, {y, ycol}];
varAll = Join[wA, wB, tA, tB, pA, pB];

icn = Join[Flatten[ic], bc /. t -> 0]; eqn = 
 Join[eqs, D[bc, t]]; var1 = D[varAll, t];
{vec, mat} = CoefficientArrays[eqn, var1];
f = Inverse[mat // N] . (-vec);
sol2 = NDSolve[{Table[var1[[i]] == f[[i]], {i, Length[var1]}], icn}, 
   varAll, {t, 0, 10}];

Visualization

{plw1 = Plot[
   Evaluate[Table[w0[y], {y, ycol}] /. sol2[[1]]], {t, 0, 1}, 
   PlotLegends -> Automatic, AxesLabel -> {"t", "w"}], 
 plt1 = Plot[
   Evaluate[Table[T0[y], {y, ycol}] /. sol2[[1]]], {t, 0, 1}, 
   PlotLegends -> Automatic, AxesLabel -> {"t", "T"}], 
 plp1 = Plot[
   Evaluate[Table[P0[y], {y, ycol}] /. sol2[[1]]], {t, 0, 1}, 
   PlotLegends -> Automatic, AxesLabel -> {"t", "P"}]}

Now we can compare NDSolve solution sol1 (Red dashed lines) with colocation method solution sol2 in one plot

{Show[plw1, 
  Plot[Table[sol1[[1]][y, t], {y, ycol}], {t, 0, 1}, 
   PlotStyle -> {Red, Dashed}]], 
 Show[plt1, 
  Plot[Table[sol1[[2]][y, t], {y, ycol}], {t, 0, 1}, 
   PlotStyle -> {Red, Dashed}]], 
 Show[plp1, 
  Plot[Table[sol1[[3]][y, t], {y, ycol}], {t, 0, 1}, 
   PlotStyle -> {Red, Dashed}]]}

Note, that solutions are differ in transition zone since NDSolve can't solve original problem with incompatible ics and bcs. In wavelets base the original system has a form

x^((a - 1))*CaputoD[varAll, {t, a}]==f

To solve this system of FDEs we use predictor-corrector method described in the paper. Unfortunately this method is very slow since Max[f] is about $10^6$ and therefore time step should be very small. For example, in sol2 the first step is about 9.52239*10^-9. Predictor-corrector code is given by

 vr0 = varAll /. t -> 0; {v0, mat0} = CoefficientArrays[icn, vr0];
s0 = Inverse[mat0] . (-v0);
rul0 = Table[vr0[[i]] -> s0[[i]], {i, Length[vr0]}];
f0 = f /. t -> 0 /. rul0;
\[Alpha] = 1;
h = 10^-7; nmax = 1000; m = Length[f]; For[k = 1, k <= nmax, k++, 
 b[k] = k^\[Alpha] - (k - 1)^\[Alpha];
 a[k] = -(2*k^(\[Alpha] + 1)) + (k - 1)^(\[Alpha] + 1) + (k + 
      1)^(\[Alpha] + 1);];

Do[s[i, 0] = s0[[i]];, {i, 1, m}];
For[j = 1, j <= nmax, j++, 
   ff[j - 1] = f /. Table[varAll[[ii]] -> s[ii, j - 1], {ii, m}]; 
   Do[r[i, j] = (h^\[Alpha]*
          Sum[b[j - th]*ff[th][[i]], {th, 0, j - 1}])/
        Gamma[\[Alpha] + 1] + s0[[i]];, {i, 1, m}]; 
   ff1[j] = (f /. Table[varAll[[ii]] -> r[ii, j], {ii, m}]);
   Do[s[i, 
       j] = (h^\[Alpha]*(Sum[a[j - tH]*ff[tH][[i]], {tH, 1, j - 1}] + 
            ff1[j][[i]] + ((j - 1)^(\[Alpha] + 1) - (-\[Alpha] + j - 
                  1)*j^\[Alpha])*f0[[i]]))/Gamma[\[Alpha] + 2] + 
       s0[[i]];, {i, 1, m}];]; // AbsoluteTiming

Here $\alpha = a, 0< a \le 1$. It takes about 96s on my laptop. We can compare this solution with sol2 as follows

time = Table[j h, {j, 0, nmax + 1}];
rule = Table[
    varAll[[i]] -> s[i, j] /. t -> time[[j + 1]], {i, m}, {j, 0, 
     nmax}] // Flatten;

lstT = Table[{time[[j]], T0[ycol[[i]]] /. t -> time[[j]]} /. rule, {i,
      nn}, {j, 100, nmax, 100}] // N;
lstP = Table[{time[[j]], P0[ycol[[i]]] /. t -> time[[j]]} /. rule, {i,
      nn}, {j, 100, nmax, 100}] // N;

lstw = Table[{time[[j]], w0[ycol[[i]]] /. t -> time[[j]]} /. rule, {i,
      nn}, {j, 100, nmax, 100}] // N;

{Show[Plot[
   Evaluate[Table[w0[y], {y, ycol}] /. sol2[[1]]], {t, 0, 1 10^-3}, 
   FrameLabel -> {"t", "w"}, PlotPoints -> 200, Frame -> True], 
  ListPlot[lstw, PlotRange -> All, PlotStyle -> PointSize[.01]]], 
 Show[Plot[
   Evaluate[Table[T0[y], {y, ycol}] /. sol2[[1]]], {t, 0, 1 10^-3}, 
   FrameLabel -> {"t", "T"}, PlotPoints -> 200, Frame -> True, 
   PlotRange -> All], 
  ListPlot[lstT, PlotRange -> All, PlotStyle -> PointSize[.01]]], 
 Show[Plot[
   Evaluate[Table[P0[y], {y, ycol}] /. sol2[[1]]], {t, 0, 1 10^-3}, 
   PlotLegends -> Automatic, FrameLabel -> {"t", "P"}, 
   PlotPoints -> 200, Frame -> True, PlotRange -> All], 
  ListPlot[lstP, PlotRange -> All, PlotStyle -> PointSize[.01]]]}

The agreement is good, but to pass transition zone we need about 10^6 steps with h=10^-7.

Update 1. We also can solve this problem using 2D colocation method, and the Euler wavelets on y, and the Haar wavelets on t as follows

UE[m_, t_] := EulerE[m, t];
psi[k_, n_, m_, t_] := 
  Piecewise[{{2^(k/2) UE[m, 2^k t - 2 n + 1], (n - 1)/2^(k - 1) <= t <
       n/2^(k - 1)}, {0, True}}];
PsiE[k_, M_, t_] := 
 Flatten[Table[psi[k, n, m, t], {n, 1, 2^(k - 1)}, {m, 0, M - 1}]]
k0 = 2; M0 = 4; With[{k = k0, M = M0}, 
 nn = Length[Flatten[Table[1, {n, 1, 2^(k - 1)}, {m, 0, M - 1}]]]];
dx = 1/(nn); xl = Table[l*dx, {l, 0, nn}]; ycol = 
 Table[(xl[[l - 1]] + xl[[l]])/2, {l, 2, nn + 1}]; Psijk = 
 With[{k = k0, M = M0}, PsiE[k, M, t1]]; Int1 = 
 With[{k = k0, M = M0}, Integrate[PsiE[k, M, t1], t1]];
Int2 = Integrate[Int1, t1]; Int3 = Integrate[Int2, t1]; Int4 = 
 Integrate[Int3, t1];
Psi[y_] := Psijk /. t1 -> y; int1[y_] := Int1 /. t1 -> y;
int2[y_] := Int2 /. t1 -> y; int3[y_] := Int3 /. t1 -> y;
int4[y_] := Int4 /. t1 -> y;
wA = Table[wa[i][t], {i, nn}]; wB = Table[wb[i][t], {i, 4}];
w4[y_] := wA . Psi[y]; w3[y_] := wA . int1[y] + wB[[1]];
w2[y_] := wA . int2[y] + wB[[1]] y + wB[[2]];
w1[y_] := wA . int3[y] + wB[[1]] y^2/2 + wB[[2]] y + wB[[3]];
w0[y_] := 
  wA . int4[y] + wB[[1]] y^3/6 + wB[[2]] y^2/2 + wB[[3]] y + wB[[4]];
tA = Table[ta[i][t], {i, nn}]; tB = Table[tb[i][t], {i, 2}];
T2[y_] := tA . Psi[y]; T1[y_] := tA . int1[y] + tB[[1]];
T0[y_] := tA . int2[y] + tB[[1]] y + tB[[2]]; pA = 
 Table[pa[i][t], {i, nn}]; pB = Table[pb[i][t], {i, 2}];
P2[y_] := pA . Psi[y]; P1[y_] := pA . int1[y] + pB[[1]];
P0[y_] := pA . int2[y] + pB[[1]] y + pB[[2]];
h[x_, k_, m_] := 
  WaveletPsi[HaarWavelet[], m x - k, WorkingPrecision -> Infinity];
p[x_, k_, m_] := 
  Piecewise[{{(1 + k - m*x)/m, 
     k >= 0 && 1/m + (2*k)/m - 2*x < 0 && 1/m + k/m - x >= 0 && 
      m > 0}, {(-k + m*x)/m, 
     k >= 0 && 1/m + (2*k)/m - 2*x >= 0 && k/m - x < 0 && 
      1/m + k/m - x >= 0 && m > 0}}, 0];
h1[x_] := WaveletPhi[HaarWavelet[], x, WorkingPrecision -> Infinity];
p1[x_] := Piecewise[{{1, x > 1}}, x];
pc[t_, k_, m_, q_] := 
  Piecewise[{{-(t^(1 - q)/(-1 + q)), 
     k == 0 && 1/m - 2*t >= 0 && m > 0 && t > 0 && 
      1/m - t >= 
       0}, {-((m^(-1 + q)*(1/(-k + m*t))^(-1 + q))/(-1 + q)), 
     k > 0 && 1/m + (2*k)/m - 2*t > 0 && k/m - t < 0 && m > 0 && 
      1/m + k/m - t > 
       0}, {(-t^q + 2*m*t^(1 + q) - 
        m*t*(-(1/(2*m)) + t)^q)/(t^q*(-(1/(2*m)) + t)^q*(m*(-1 + q))),
      k == 0 && m > 0 && 1/m - 2*t < 0 && 
      1/m - t >= 
       0}, {(1/(-1 + q))*((2^(-1 + q)*
          m^(-1 + 2*q)*(-(-(k/m) + t)^q - 2*k*(-(k/m) + t)^q + 
            2*m*t*(-(k/m) + t)^q + 2*k*(-((1/2 + k)/m) + t)^q - 
            2*m*t*(-((1/2 + k)/m) + t)^q))/((1 + 2*k - 2*m*t)*(k - 
             m*t))^q), 
     k > 0 && 1/m + (2*k)/m - 2*t == 0 && m > 0 && 
      1/m + k/m - t > 
       0}, {-((1/(-1 + q))*((2^(-1 + q)*
            m^(-1 + 2*q)*(-2*(-((1/2 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(k - m*t))^q - 
              2*k*(-((1/2 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(k - m*t))^q + 
              2*m*t*(-((1/2 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(k - m*t))^
                q + (-((1 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(k - m*t))^q + 
              2*k*(-((1 + k)/m) + t)^q*((1 + 2*k - 2*m*t)*(k - m*t))^
                q - 2*m*t*(-((1 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(k - m*t))^q + (-(k/m) + t)^
                q*((1 + 2*k - 2*m*t)*(1 + k - m*t))^q + 
              2*k*(-(k/m) + t)^q*((1 + 2*k - 2*m*t)*(1 + k - m*t))^
                q - 2*m*t*(-(k/m) + t)^
                q*((1 + 2*k - 2*m*t)*(1 + k - m*t))^q - 
              2*k*(-((1/2 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(1 + k - m*t))^q + 
              2*m*t*(-((1/2 + k)/m) + t)^
                q*((1 + 2*k - 2*m*t)*(1 + k - m*t))^
                q))/(((1 + 2*k - 2*m*t)*(k - m*t))^
             q*((1 + 2*k - 2*m*t)*(1 + k - m*t))^q))), 
     k > 0 && m > 0 && 1/m + (2*k)/m - 2*t <= 0 && 
      1/m + k/m - t <= 
       0}, {-((1/(2*
            m*(-1 + q)))*((2^q*m^(2*q)*
             t^q*(-(1/m) + t)^q*(-(1/(2*m)) + t)^q - 
            2^(1 + q)*m^(1 + 2*q)*
             t^(1 + q)*(-(1/m) + t)^q*(-(1/(2*m)) + t)^q - 
            2^(1 + q)*m^(2*q)*t^q*(-(1/(2*m)) + t)^(2*q) + 
            2^(1 + q)*m^(1 + 2*q)*t^(1 + q)*(-(1/(2*m)) + t)^(2*q) + 
            t^q*((-1 + m*t)*(-1 + 2*m*t))^q - 
            2*m*t^(1 + q)*((-1 + m*t)*(-1 + 2*m*t))^q + 
            2*m*t*(-(1/(2*m)) + t)^q*((-1 + m*t)*(-1 + 2*m*t))^q)/(t^
             q*(-(1/(2*m)) + t)^q*((-1 + m*t)*(-1 + 2*m*t))^q))), 
     k == 0 && 1/m - 2*t < 0 && 1/m - t < 0 && 
      m > 
       0}, {(1/(-1 + q))*((2^(-1 + q)*
          m^(-1 + q)*((-m^q)*(-(k/m) + t)^q - 
            2*k*m^q*(-(k/m) + t)^q + 2*m^(1 + q)*t*(-(k/m) + t)^q + 
            2*k*m^q*(-((1/2 + k)/m) + t)^q - 
            2*m^(1 + q)*
             t*(-((1/2 + k)/m) + t)^q - ((1 + 2*k - 2*m*t)*(k - m*t))^
              q*(1/(-1 - 2*k + 2*m*t))^q - 
            2*k*((1 + 2*k - 2*m*t)*(k - m*t))^
              q*(1/(-1 - 2*k + 2*m*t))^q + 
            2*m*t*((1 + 2*k - 2*m*t)*(k - m*t))^
              q*(1/(-1 - 2*k + 2*m*t))^q))/((1 + 2*k - 2*m*t)*(k - 
             m*t))^q), 
     1/m + (2*k)/m - 2*t < 0 && k > 0 && m > 0 && 1/m + k/m - t > 0}},
    0];
pc1[t_, q_] := 
  Piecewise[{{-(t^(1 - q)/(-1 + q)), 
     t <= 1}}, -(((-1 + t)^q*t + t^q - t^(1 + q))/((-1 + t)^q*
        t^q*(-1 + q)))];

J = 3; M = 2^J;
dt = 1/(2*M); tl = Table[l dt, {l, 0, 2 M}];
Tcol = Table[(tl[[l - 1]] + tl[[l]])/2, {l, 2, 2 M + 1}];
U1[k_][t_, q_] := 
  Sum[v[k][i, j] pc[t, i, 2^j, q], {j, 0, J, 1}, {i, 0, 2^j - 1, 1}] +
    v1[k] pc1[t, q];
U0[k_][t_] := 
  Sum[v[k][i, j] p[t, i, 2^j], {j, 0, J, 1}, {i, 0, 2^j - 1, 1}] + 
   v1 [k] p1[t] + v2[k];

eqw = With[{w = w0[y], T = T0[y], 
    P = P0[y]}, (D[w, t] == w1[y] + w2[y] - w4[y] - w - T - P + 1)];
eqnw = Table[eqw, {y, ycol}];
eqT = With[{w = w0[y], T = T0[y], P = P0[y]}, 
   D[T, t] == (D[T, y] + (1 + (T + 1)^3)*T2[y] + 
      3*(T + 1)^2*T1[y]^2 + (w1[y]^2 + w2[y]^2 + w^2) + T1[y]*P1[y] + 
      T1[y]^2)];
eqnT = Table[eqT, {y, ycol}];
eqP = With[{w = w0[y], T = T0[y], P = P0[y]}, 
  D[P, t] == (P1[y] + P2[y] + T2[y])]; eqnP = 
 Table[eqP, {y, ycol}]; eqs = Join[eqnw, eqnT, eqnP];
bc0 = With[{w = w0[y], T = T0[y], P = P0[y]}, 
  Join[{w == 0, w2[y] == 0, T == Exp[-100 t], P == 1 - Exp[-100 t]} /. 
    y -> 0, {w == 0, w2[y] == 0, T == 1, P == 0} /. y -> 1]]; bc = 
 With[{w = w0[y], T = T0[y], P = P0[y]}, 
  Join[{w == 0, w2[y] == 0, T == 0, P == 1} /. 
    y -> 0, {w == 0, w2[y] == 0, T == 1, P == 0} /. y -> 1]];
icy = With[{w = w0[y], T = T0[y], 
   P = P0[y]}, {w == 0, T == 1, P == 0} /. t -> 0]; ic = 
 Table[icy, {y, ycol}];
varAll = Join[wA, wB, tA, tB, pA, pB];
icn = Join[Flatten[ic], bc0 /. t -> 0]; eqn = 
 Join[eqs, D[bc0, t]]; var1 = D[varAll, t];
{vec, mat} = CoefficientArrays[eqn, var1];
f = Inverse[mat // N] . (-vec); vr0 = varAll /. t -> 0; {v0, mat0} = 
 CoefficientArrays[icn, vr0];
s0 = Inverse[mat0] . (-v0);
rul0 = Table[vr0[[i]] -> s0[[i]], {i, Length[vr0]}];
f0 = f /. t -> 0 /. rul0; m = Length[f]; sol2 = 
 NDSolve[{Table[var1[[i]] == f[[i]], {i, Length[var1]}], icn}, 
  varAll, {t, 0, 1}]; fmax = Max[Abs[f0]];

solCom[tm_] := 
  Module[{L = 1, tmax = tm}, df = tmax/L^2; tn = 1/Gamma[1 - q]/tmax^q;
   varM = 
    Join[Flatten[Table[{v2[k], v1[k]}, {k, m}]], 
     Flatten[Table[
       v[k][i, j], {j, 0, J, 1}, {i, 0, 2^j - 1, 1}, {k, m}]]]; 
   rult = Table[varAll[[k]] -> U0[k][t], {k, m}];
   eq[q_] := 
    Flatten[Table[
      U1[k][t, q] == f[[k]]/tn/tmax /. rult, {t, Tcol}, {k, m}]]; 
   ict = Table[U0[k][0] == s0[[k]], {k, m}];
   Do[sol[q] = 
      FindRoot[Join[eq[q], ict], 
       Table[{varM[[i]], 1/10}, {i, Length[varM]}], 
       Method -> {"Newton", "StepControl" -> "TrustRegion"}, 
       MaxIterations -> 100];, {q, {4/5, 3/5, 2/5}}]; 
   Table[sol[q], {q, {4/5, 3/5, 2/5}}]];

solC1 = solCom[1]; // AbsoluteTiming

pl1 = Plot[
  Evaluate[
   Join[{w0[y] /. sol2[[1]]}, 
     Table[  w0[y] /. rult /. solC1[[i]], {i, 3}]] /. t -> 1], {y, 0, 
   1}, PlotLegends -> 
   Table[Row[{"\[Alpha] =", q0}], {q0, {1, 0.8, 0.6, 0.4}}], 
  AxesLabel -> {"y", "w"}, PlotRange -> All]

First of thanks for your efforts. How to plot w vs y for t=1 and a=0.4,1? — zhk, Commented Jan 26, 2023 at 6:12
If the final solution is an interpolating function then it would be easy to use it for different purposes. — zhk, Commented Jan 26, 2023 at 6:22
First, we need to reduce computation time in 1000 times to pass transition zone. Second, we can use interpolation function in a form W=Interpolation[lstw]. — Alex Trounev, Commented Jan 26, 2023 at 7:24
If i try alpha =0.4 then it gives General::ovfl: Overflow occurred in computation. — zhk, Commented Jan 26, 2023 at 7:53
@zhk Please, pay attention, that in numerical model there is $h^{\alpha} f$ in Sum . Since Max[Abs[f]] is about 10^6, we need constraint $h^{\alpha}max( |f|)<1$. In a case of $\alpha=1$ we have h=10^-7. In a case of $\alpha =0.4$ we should take h=3 10^-18. It is why I ask you above how we can handle jumps. In this case jumps is about 10^6. Normally we use this algorithm when Max[Abs[f]] is about 1. — Alex Trounev, Commented Jan 26, 2023 at 8:22

3 revs, 2 users 60% · Accepted Answer · 2023-01-17 03:55:46Z

Solving fractional differential equation (FDE) numerically is a pain at least for now (version 13.2) because there's no built-in support in NDSolve. One may guess there's a hidden feature somewhere, but using a function obtained from this answer for version 13.2, nothing related is found:

Mathematica graphics

There does exist some trial on building solver for numeric FDE in this site, see:

Numerical solution for a non-linear Fractional Differential Equation (FDE)

Fractional PDE with CaputoD

Solving a Caputo fractional diffusion equation in cylindrical coordinates

But none of them is good enough (compared with other built-in methods of NDSolve).

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