Changed plot y-axis labels to more accurately express the values. (#34)

I think it would be a good idea to update the y-axis labels from "Pr" to
something like "Sqrt(Pr)" to reflect the actual values.

As of now, it is confusing to see "Pr" for a set of values which do not
add up to 1.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/mqt/qudits/visualisation/plot_information.py

@@ -11,25 +11,44 @@
 
 
 class HistogramWithErrors:
-    def __init__(self, labels, counts, errors, title="Simulation") -> None:
+    def __init__(self, labels, counts, errors, title="", xlabel="Labels", ylabel="Counts") -> None:
         self.labels = labels
         self.counts = counts
         self.errors = errors
+
         self.title = title
+        self.xlabel = xlabel
+        self.ylabel = ylabel
 
     def generate_histogram(self) -> None:
-        plt.bar(self.labels, self.counts, yerr=self.errors, capsize=5, color="b", alpha=0.7, align="center")
-        plt.xlabel("States")
-        plt.ylabel("Pr")
+        plt.bar(
+            self.labels,
+            self.counts,
+            yerr=self.errors,
+            capsize=5,
+            color="b",
+            alpha=0.7,
+            align="center",
+        )
+        plt.xlabel(self.xlabel)
+        plt.ylabel(self.ylabel)
         plt.title(self.title)
         plt.xticks(rotation=45, ha="right")
         plt.tight_layout()
         plt.show()
 
     def save_to_png(self, filename) -> None:
-        plt.bar(self.labels, self.counts, yerr=self.errors, capsize=5, color="b", alpha=0.7, align="center")
-        plt.xlabel("States")
-        plt.ylabel("Pr")
+        plt.bar(
+            self.labels,
+            self.counts,
+            yerr=self.errors,
+            capsize=5,
+            color="b",
+            alpha=0.7,
+            align="center",
+        )
+        plt.xlabel(self.xlabel)
+        plt.ylabel(self.ylabel)
         plt.title(self.title)
         plt.xticks(rotation=45, ha="right")
         plt.tight_layout()
@@ -58,34 +77,21 @@ def state_labels(circuit):
     return string_states
 
 
-def plot_state(result: np.ndarray, circuit: QuantumCircuit, errors=None) -> None:
-    result = np.squeeze(result).tolist()
-    if errors is None:
-        errors = len(result) * [0]
+def plot_state(state_vector: np.ndarray, circuit: QuantumCircuit, errors=None) -> None:
+    labels = state_labels(circuit)
 
-    string_states = state_labels(circuit)
+    state_vector_list = np.squeeze(state_vector).tolist()
+    counts = [abs(coeff) for coeff in state_vector_list]
 
-    result = [abs(coeff) for coeff in result]
-    h_plotter = HistogramWithErrors(string_states, result, errors, title="Simulation")
+    h_plotter = HistogramWithErrors(labels, counts, errors, title="Simulation", xlabel="States", ylabel="Sqrt(Pr)")
     h_plotter.generate_histogram()
 
 
-def plot_counts(result, circuit: QuantumCircuit) -> None:
-    custom_labels = state_labels(circuit)
-
-    # Count the frequency of each outcome
-    counts = {label: result.count(i) for i, label in enumerate(custom_labels)}
-
-    # Create a bar plot with custom labels
-    plt.bar(custom_labels, counts.values())
+def plot_counts(measurements, circuit: QuantumCircuit) -> None:
+    labels = state_labels(circuit)
+    counts = [measurements.count(i) for i in range(len(labels))]
 
-    # Add labels and title
-    plt.xlabel("States")
-    plt.ylabel("Counts")
-    plt.title("Simulation")
+    errors = len(labels) * [0]
 
-    plt.xticks(rotation=45, ha="right")
-    plt.tight_layout()
-    plt.show()
-
-    return counts
+    h_plotter = HistogramWithErrors(labels, counts, errors, title="Simulation", xlabel="States", ylabel="Counts")
+    h_plotter.generate_histogram()