Conditional I/O

yggdrasil also supports conditional input/output logic within the YAML specification file to allow a model to send/receive output/input to/from different destinations/sources based on the value of an input/output variable. yggdrasil supports both basic logic (e.g. less than, equal to) and more complex methods for evaluating the state implemented via Python functions.

Conditional Output

In the example below, the process represented by model B changes depending on the value of the input so that we can represent the relationship as a piecewise set of two functions with each one being valid under different conditions. In this case modelB_function1 is only valid if the input is <=2 and modelB_function2 is only valid if the input is >2.

Model Code:

def modelA_function(in_val):
    out_val = in_val
    print("modelA_function(%s) = %s" % (in_val, out_val))
    return out_val

def modelB_function1(in_val):
    # Only valid if in_val <= 2
    out_val = in_val**2
    print("modelB_function1(%s) = %s" % (in_val, out_val))
    return in_val, out_val

def modelB_function2(in_val):
    # Only valid if in_val > 2
    out_val = 2 * in_val**2
    print("modelB_function2(%s) = %s" % (in_val, out_val))
    return in_val, out_val


def condition_function2(in_val):
    return (in_val > 2)

(Example in other languages)

To instruct yggdrasil to pass output from model A to the correct model B function under the required conditions, the YAML should contain a connection to both model B function inputs with the filter parameter added to both.

Model YAML:

models:
  - name: python_modelA
    language: python
    args: ./src/conditional_io_modelA.py
    function: modelA_function

  - name: python_modelB1
    language: python
    args: ./src/conditional_io_modelB1.py
    function: modelB_function1

  - name: python_modelB2
    language: python
    args: ./src/conditional_io_modelB2.py
    function: modelB_function2

connections:
  - input: ./Input/input.txt  # Connection between file and model A input
    output: python_modelA:input
    filetype: table
  - input: python_modelA:output  # Connection between model A output & model B input
    outputs:
      - name: python_modelB1:input
        filter:
          statement: "%x% <= 2"
      - name: python_modelB2:input
        filter:
          function: ./src/conditional_io_modelB2.py:condition_function2
  - inputs:
      - python_modelB1:output  # Connection between model B, function 1 output and file
      - python_modelB2:output  # Connection between model B, function 2 output and file
    output: ./output.txt
    filetype: table
    field_names: InputMass,Mass
    field_units: g,g**2
    format_str: "%.1lf\t%.1lf\n"

(Example in other languages)

filter values are maps with either statement or function parameters (see here) and any additional filter parameters (see here). statement filters are simple expressions of equality/inequality (in Python syntax) that reference the connection input as %x% (e.g. the filter for python_modelB1:input above). Alternatively, you can provide a value for the function parameter which encodes a filter using a Python function. function values should be of the form <filename>:<function name> where filename is the full path to the location of a Python source file containing the desired function that should be used to determine if the condition is satisfied and function name is the name of the desired function (e.g. the filter for python_modelB2:input above). Functions used in such cases should take a single argument (the variable or tuple of variables being passed by the connection), and return a boolean (the validity of the condition being represented). The path to the file containing the function can be absolute or relative to the directory containing the yaml file.

Filter Options

General Filter Options

Option	Type	Required	Description
filtertype	string		Pass every message (Options described here)

Filter Types

Filtertype	Description
direct	Pass every message
function	Filter messages based on a function
statement	Filter messages based on a statement

Type Specific Filter Options

Option	Type	Valid For ‘Filtertype’ Of	Description
function	function	[‘function’]	The handle for a callable Python object (e.g. function) that should be used to determine if a message should be filtered or a string of the form “<function file>:<function name>” identifying a function where “<function file>” is the module or Python file containing the function and “<function name>” is the name of the function. The function should take the message as input and return a boolean, True if the message should pass through the filter, False if it should not.
statement	string	[‘statement’]	Python statement in terms of the message as represented by the string “%x%” that should evaluate to a boolean, True if the message should pass through the filter, False if it should not. The statement should only use a limited set of builtins and the math library (See yggdrasil.tools.safe_eval). If more complex relationships are required, use the FunctionFilter class.