Fix init_model_old_ratio for multitask (deepmodeling#221)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
  - Enhanced data initialization to support multiple tasks.
- Improved handling of multitask configurations for more accurate
calculations.
  - Updated input script generation for better automation.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: zjgemi <[email protected]>

dpgen2/op/run_dp_train.py

@@ -280,7 +280,13 @@ def execute(
         auto_prob_str = "prob_sys_size"
         if do_init_model:
             old_ratio = config["init_model_old_ratio"]
-            numb_old = len(init_data) + len(iter_data_old_exp)
+            if config["multitask"]:
+                head = config["head"]
+                multi_init_data_idx = config["multi_init_data_idx"]
+                len_init = len(multi_init_data_idx[head])
+            else:
+                len_init = len(init_data)
+            numb_old = len_init + len(iter_data_old_exp)
             numb_new = numb_old + len(iter_data_new_exp)
             auto_prob_str = f"prob_sys_size; 0:{numb_old}:{old_ratio}; {numb_old}:{numb_new}:{1.-old_ratio:g}"
 
@@ -418,6 +424,7 @@ def write_data_to_input_script(
                     ]
                 if k == head:
                     v["training_data"]["systems"] += [str(ii) for ii in iter_data]
+                    v["training_data"]["auto_prob"] = auto_prob_str
             return odict
         data_list = [str(ii) for ii in init_data] + [str(ii) for ii in iter_data]
         if major_version == "1":