first draft; no tests

Author: tim-at-topos

packages/catlog/src/stdlib/analyses/mod.rs

@@ -4,3 +4,4 @@
 pub mod ode;
 
 pub mod reachability;
+pub mod signed_links_to_signed_cat;

packages/catlog/src/stdlib/analyses/signed_links_to_signed_cat.rs

@@ -0,0 +1,91 @@
+//! Migration for going from categories with signed links to signed categories
+//  (e.g. from signed stock-flow diagrams to causal loop diagrams)
+
+use crate::dbl::discrete_tabulator::theory::TabMorType;
+use crate::dbl::discrete_tabulator::theory::TabObType;
+use std::rc::Rc;
+
+use crate::dbl::discrete::model::DiscreteDblModel;
+use crate::dbl::discrete_tabulator::model::DiscreteTabModel;
+use crate::dbl::model::{FgDblModel, MutDblModel};
+use crate::one::category::FgCategory;
+use crate::one::path::Path;
+use crate::stdlib::theories;
+use crate::zero::name;
+
+/** Span-migration for categories with signed links.
+ *  
+ *  We create a CLD from a category with signed links from the query defined on
+ *  objects as
+ *  
+ *  V  |-> stock : S | flow : F
+ *  E+ |-> out : F   | link : L+
+ *  E- |-> in : F    | link : L-
+ *
+ *  and on morphisms as (...) something that will be written up eventually, but
+ *  in short can be described quite simply in words:
+ *
+ *    - For each stock, create a vertex
+ *    - For each flow, create a (+,-)-span, where the apex is a new vertex
+ *      corresponding to the flow, and there is a negative arrow to the (vertex
+ *      corresponding to the) source of the flow, and a positive arrow to the
+ *      (vertex corresponding to the) target of the flow
+ *    - For each (signed) link, create an arrow (of the same sign) from the
+ *      (vertex corresponding to the) source stock to the (vertex corresponding
+ *      to the) target flow
+ */
+pub fn migrate(model: DiscreteTabModel) -> DiscreteDblModel {
+    let mut migrated_model: DiscreteDblModel =
+        DiscreteDblModel::new(Rc::new(theories::th_signed_category()));
+
+    let stock_type = TabObType::Basic(name("Object"));
+    let flow_type = TabMorType::Hom(Box::new(stock_type.clone()));
+    let pos_link_type = TabMorType::Basic(name("Link"));
+    let neg_link_type = TabMorType::Basic(name("NegativeLink"));
+
+    // Create an object for each stock (a "stock-object")
+    for s in model.ob_generators() {
+        migrated_model.add_ob(s.clone(), name("Object"));
+    }
+
+    // Create a span for each flow
+    for f in model.mor_generators_with_type(&flow_type) {
+        // An object for each flow (a "flow-object")
+        migrated_model.add_ob(f.clone(), name("Object"));
+        // A negative link from the flow object to the flow-source object
+        migrated_model.add_mor(
+            format!("{}_in", f).as_str().into(),
+            f.clone(),
+            model.mor_generator_dom(&f).unwrap_basic(),
+            Path::Id(name("Object")),
+        );
+        // A positive link from the flow object to the flow-target object
+        migrated_model.add_mor(
+            format!("{}_in", f).as_str().into(),
+            f.clone(),
+            model.mor_generator_cod(&f).unwrap_basic(),
+            name("Negative").into(),
+        );
+    }
+
+    // Create a positive arrow for each positive link
+    for pl in model.mor_generators_with_type(&pos_link_type) {
+        migrated_model.add_mor(
+            pl.clone(),
+            model.mor_generator_dom(&pl).unwrap_basic(),
+            model.mor_generator_cod(&pl).unwrap_basic(),
+            Path::Id(name("Object")),
+        );
+    }
+    // Create a negative arrow for each negative link
+    for nl in model.mor_generators_with_type(&neg_link_type) {
+        migrated_model.add_mor(
+            nl.clone(),
+            model.mor_generator_dom(&nl).unwrap_basic(),
+            model.mor_generator_cod(&nl).unwrap_basic(),
+            name("Negative").into(),
+        );
+    }
+
+    migrated_model
+}