why ode45 can not substitute y(2) with initial value

function dy = Weeq(t,y)

global K rs rr zpgs Tm Te Wm Pd global Ivdot Igdot Iedot C

Wg = y(2).*(zpgs+1) - y(1).*zpgs

eq1Tm = ((rr+rs).^(2)./(rr.*Iedot) + rs.^(2)./(rr.*Igdot));

eq1Te = (rr+rs)./Iedot;

eq1Tg = rs./Igdot;

eq1C = ((rr+rs).^(2)./(rr.*Iedot.*K) + rs.^(2)./(rr.*Igdot.*K));

eq1Wr = (Ivdot.*(rr+rs).^(2)./(rr.*Iedot.*K) + Ivdot.*rs.^(2)./(rr.*Igdot.*K)+rr);

Tg = (Pd - Tm.*Wm -Te.* y(2))./Wg

eq1 = (eq1Tm.*Tm + eq1Te.*Te + eq1Tg.*Tg - eq1C.*C)./eq1Wr;

eq2Tm = K.*rr./Ivdot;

eq2Te = rr^(2).*K./((rr+rs).*Ivdot) + (rs^(2)./((rr+rs).*Igdot));

eq2Tg = rs./Igdot;

eq2C = rr./Ivdot;

eq2We = rr^(2).*K.*Iedot./((rr+rs).*Ivdot) + (rs^(2).*Iedot./((rr+rs).*Igdot)) + rr + rs;

eq2 = (eq2Tm.*Tm + eq2Te.*Te - eq2Tg.*Tg - eq2C.*C)./eq2We;

dy=[eq1 ; eq2]

---------

sim.m file

Wei = 80.935 Wri = 58.453 Tm = [5] Te = 60 S = 1

[t,y] = ode15s(@Weeq,[0,100],[Wri; Wei])

then result is

Wei =

   80.9350

Wri =

   58.4530

Tm =

     5

Te =

    60

S =

     1

Tg =

     []

dy =

     []

Error using odearguments (line 93) WEEQ returns a vector of length 0, but the length of initial conditions vector is 2. The vector returned by WEEQ and the initial conditions vector must have the same number of elements.

Error in ode15s (line 149) [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

Error in ode (line 34) [t,y] = ode15s(@Weeq,[0,100],[Wri; Wei])

why matlab cannot replace y(2) with initial value for evaluating Tg??? if true % code end

[Jan]

Please format your code properly to improve the readability.

Answer 1

[Jan]

When any of the (too!) many global variables is empty, the result of the computations can be empty also. So please use the debugger (set a break point) to check the values of:

K rs rr zpgs Tm Te Wm Pd
Ivdot Igdot Iedot C

But please read this: http://www.mathworks.de/matlabcentral/answers/1971