Allow initial = None in SIRT (#1906)

---------

Signed-off-by: Margaret Duff <43645617+MargaretDuff@users.noreply.github.com>

CHANGELOG.md

@@ -15,6 +15,7 @@
     - Add checks on out argument passed to processors to ensure corrrect dtype and size (#1805)
     - Internal refactor: Replaced string-based label checks with enum-based checks for improved type safety and consistency (#1692)
     - Internal refactor: Separate framework into multiple files (#1692)
+    - Allow the SIRT algorithm to take `initial=None` (#1906)
   - Testing:
     - New unit tests for operators and functions to check for in place errors and the behaviour of `out` (#1805)
     - Updates in SPDHG vs PDHG unit test to reduce test time and adjustments to parameters (#1898)

Wrappers/Python/cil/optimisation/algorithms/SIRT.py

@@ -50,7 +50,7 @@ class SIRT(Algorithm):
     ----------
 
     initial : DataContainer, default = None
-        Starting point of the algorithm, default value = Zero DataContainer
+        Starting point of the algorithm, default value =  DataContainer in the domain of the operator allocated with zeros. 
     operator : LinearOperator
         The operator A.
     data : DataContainer
@@ -91,7 +91,7 @@ class SIRT(Algorithm):
     """
 
 
-    def __init__(self, initial, operator, data, lower=None, upper=None, constraint=None, **kwargs):
+    def __init__(self, initial=None, operator=None, data=None, lower=None, upper=None, constraint=None, **kwargs):
 
         super(SIRT, self).__init__(**kwargs)
 
@@ -100,6 +100,23 @@ def __init__(self, initial, operator, data, lower=None, upper=None, constraint=N
     def set_up(self, initial, operator, data, lower=None, upper=None, constraint=None):
         """Initialisation of the algorithm"""
         log.info("%s setting up", self.__class__.__name__)
+
+        warning = 0
+        if operator is None:
+            warning += 1
+            msg = "an `operator`"
+        if data is None:
+            warning += 10
+            if warning > 10:
+                msg += " and `data`"
+            else:
+                msg = "`data`"
+        if warning > 0:
+            raise ValueError(f'You must pass {msg} to the SIRT algorithm' )
+
+        if initial is None:
+            initial = operator.domain_geometry().allocate(0)
+
         self.x = initial.copy()
         self.tmp_x = self.x * 0.0
         self.operator = operator

Wrappers/Python/test/test_algorithms.py

@@ -979,6 +979,53 @@ def setUp(self):
 
     def tearDown(self):
         pass
+
+    def test_set_up(self):
+
+        initial = self.A2.domain_geometry().allocate(0)
+        sirt = SIRT(initial=initial, operator=self.A2, data=self.b2, lower=0, upper=1)
+
+        # Test if set_up correctly configures the object
+        self.assertTrue(sirt.configured)
+        self.assertIsNotNone(sirt.x)
+        self.assertIsNotNone(sirt.r)
+        self.assertIsNotNone(sirt.constraint)
+        self.assertEqual(sirt.constraint.lower, 0)
+        self.assertEqual(sirt.constraint.upper, 1)
+
+
+        constraint = IndicatorBox(lower=0, upper=1)
+        sirt = SIRT(initial=None, operator=self.A2, data=self.b2, constraint=constraint)
+
+        # Test if set_up correctly configures the object with constraint
+        self.assertTrue(sirt.configured)
+        self.assertEqual(sirt.constraint, constraint)
+
+
+        with self.assertRaises(ValueError) as context:
+            sirt = SIRT(initial=None, operator=None, data=self.b2)
+            self.assertEqual(str(context.exception), 'You must pass an `operator` to the SIRT algorithm')
+
+
+        with self.assertRaises(ValueError) as context:
+            sirt = SIRT(initial=None, operator=self.A2, data=None)
+            self.assertEqual(str(context.exception), 'You must pass `data` to the SIRT algorithm')
+        with self.assertRaises(ValueError) as context:  
+            sirt = SIRT(initial=None, operator=None, data=None)  
+            self.assertEqual(str(context.exception), 
+                'You must pass an `operator` and `data` to the SIRT algorithm')  
+
+        sirt = SIRT(initial=None, operator=self.A2, data=self.b2)
+        self.assertTrue(sirt.configured)
+        self.assertIsInstance(sirt.x, ImageData)
+        self.assertTrue((sirt.x.as_array() == 0).all())
+
+
+        initial = self.A2.domain_geometry().allocate(1)
+        sirt = SIRT(initial=initial, operator=self.A2, data=self.b2)
+        self.assertTrue(sirt.configured)
+        self.assertIsInstance(sirt.x, ImageData)
+        self.assertTrue((sirt.x.as_array() == 1).all())
 
     def test_update(self):
         # sirt run 5 iterations