Autowrapping Model Functions

If your model can be expressed as a function in one of the supported languages, yggdrasil can automatically create the wrapper to make calls to the interface. In the example below, the two models being connected are just functions with one input and one output.

Model Code:

1def model_function(in_buf):
2    print("Model A: %s" % in_buf)
3    out_buf = in_buf
4    return out_buf

1def model_function(in_buf):
2    print("Model B: %s" % in_buf)
3    out_buf = in_buf
4    return out_buf

(Example in other languages)

In order to allow yggdrasil to wrap model functions, the corresponding entry in the YAML specification file should include a value for the function parameter which should be the name of the model function within the model file (provided via the args parameter). If no inputs or outputs are provided, yggdrasil will attempt to parse the definition for the target model function in order to determine the model’s inputs and outputs. If inputs and/or outputs are provided in the YAML they must either match the number of inputs and/or outputs in the function defintion (as below) or there must only be one and all of the model’s inputs and/or outputs will be bundled as an array.

Model YAML:

 1models:
 2  - name: python_modelA
 3    language: python
 4    args: ./src/model_function_modelA.py
 5    function: model_function
 6    inputs: inputA
 7    outputs: outputA
 8
 9  - name: python_modelB
10    language: python
11    args: ./src/model_function_modelB.py
12    function: model_function
13    inputs: inputB
14    outputs: outputB
15
16connections:
17  - input: outputA  # Connection between model A output & model B input
18    output: inputB
19  - input: ./Input/input.txt  # Connection between file and model A input
20    output: inputA
21  - input: outputB  # Connection between model B output and file
22    output: ./output.txt

(Example in other languages)

Notes on Autowrapping C/C++ Model Functions

The autowrapping of C/C++ models differs from other languages in several respects.

  1. The output variables are expected to be assigned by pointers as inputs (or references in the case of C++). yggdrasil assumes that no input variables come after the output variables.

  2. For C models, the user must explicitly specify the names of the output variables as it is not possible for yggdrasil to determine whether a variable is an input or output based on the function definition alone since input variables can also be pointers. In the case of C++ models, yggdrasil can identify output variables based on the presence of the “pass by reference” operator &. If a C++ model definition defines an output variable as a pointer instead, the user must explicitly declare the output variables as in the case of a C model.

  3. For input and output strings, yggdrasil assumes that the string variable (or pointer) is immediately followed by a variable (or pointer) that contains (or will contain) the string length.