Fix issue patrick-kidger#563: time t0 instead of 0 is passed to _chec…

…k in _assert_term_compatible, so the term is not required to be well-defined at time 0, but rather at time t0.

diffrax/_integrate.py

@@ -119,6 +119,7 @@ def _is_none(x: Any) -> bool:
 
 
 def _assert_term_compatible(
+    t: FloatScalarLike,
     y: PyTree[ArrayLike],
     args: PyTree[Any],
     terms: PyTree[AbstractTerm],
@@ -138,7 +139,7 @@ def _check(term_cls, term, term_contr_kwargs, yi):
                 for term, arg, term_contr_kwarg in zip(
                     term.terms, get_args(_tmp), term_contr_kwargs
                 ):
-                    _assert_term_compatible(yi, args, term, arg, term_contr_kwarg)
+                    _assert_term_compatible(t, yi, args, term, arg, term_contr_kwarg)
             else:
                 raise ValueError(
                     f"Term {term} is not a MultiTerm but is expected to be."
@@ -166,7 +167,7 @@ def _check(term_cls, term, term_contr_kwargs, yi):
             elif n_term_args == 2:
                 vf_type_expected, control_type_expected = term_args
                 try:
-                    vf_type = eqx.filter_eval_shape(term.vf, 0.0, yi, args)
+                    vf_type = eqx.filter_eval_shape(term.vf, t, yi, args)
                 except Exception as e:
                     raise ValueError(f"Error while tracing {term}.vf: " + str(e))
                 vf_type_compatible = eqx.filter_eval_shape(
@@ -178,7 +179,7 @@ def _check(term_cls, term, term_contr_kwargs, yi):
                 contr = ft.partial(term.contr, **term_contr_kwargs)
                 # Work around https://github.com/google/jax/issues/21825
                 try:
-                    control_type = eqx.filter_eval_shape(contr, 0.0, 0.0)
+                    control_type = eqx.filter_eval_shape(contr, t, t)
                 except Exception as e:
                     raise ValueError(f"Error while tracing {term}.contr: " + str(e))
                 control_type_compatible = eqx.filter_eval_shape(
@@ -1077,6 +1078,7 @@ def _promote(yi):
     if isinstance(solver, (EulerHeun, ItoMilstein, StratonovichMilstein)):
         try:
             _assert_term_compatible(
+                t0,
                 y0,
                 args,
                 terms,
@@ -1098,6 +1100,7 @@ def _promote(yi):
 
     # Error checking for term compatibility
     _assert_term_compatible(
+        t0,
         y0,
         args,
         terms,