fixes #46 and inconsistency

Author: TorBorve

src/analysis/frequency_response.rs

@@ -195,6 +195,11 @@ fn freq_response_ss_mat(
     assert_eq!(m, 1, "Function is only tested for SISO systems");
     assert_eq!(p, 1, "Function is only tested for SISO systems");
 
+    if n == 0 {
+        let res = DMatrix::from_iterator(p, m, d.iter().map(|&x| c64(x, 0.0)));
+        return Ok(res);
+    }
+
     let baleig = CString::new("A").unwrap(); // balance A and compute condition number
     let inita = CString::new("G").unwrap(); // general A matrix
 
@@ -272,7 +277,7 @@ fn freq_response_ss_mat(
 
 #[cfg(test)]
 mod tests {
-    use crate::{FrequencyResponse, Tf};
+    use crate::{Continuous, FrequencyResponse, Ss, Tf, utils::traits::Mag2Db};
 
     use super::log_space;
     use approx::assert_abs_diff_eq;
@@ -317,4 +322,15 @@ mod tests {
             assert_abs_diff_eq!(res_tf.im, res_tf.im, epsilon = 1e-3);
         }
     }
+
+    #[test]
+    fn ss_freq_resp_edge_cases() {
+        let gain = 3.0;
+        let ss = Ss::<Continuous>::new_from_scalar(gain);
+        let mag_phase_freq = ss.bode(0.1, 10.);
+        for [mag, phase, _] in mag_phase_freq {
+            assert_abs_diff_eq!(mag, gain.mag2db(), epsilon = 1e-6);
+            assert_abs_diff_eq!(phase, 0.);
+        }
+    }
 }

src/systems/state_space.rs

@@ -394,7 +394,7 @@ impl<U: Time + 'static> Ss<U> {
     /// # Panics
     /// This function will panic if the input-output dimensions of `self` and
     /// `sys2` do not match.
-    pub fn feedback(self, sys2: Self) -> Self {
+    pub fn feedback(self, sys2: &Self) -> Self {
         assert_eq!(self.ninputs(), sys2.noutputs());
         assert_eq!(self.noutputs(), sys2.ninputs());
         self.assert_valid();
@@ -960,12 +960,12 @@ mod tests {
         let ss1 = (Tf::s() / (Tf::s() + 1.0)).to_ss().unwrap();
         let ss2 = (1.0 / Tf::s()).to_ss().unwrap();
 
-        let ss_fb = ss1.clone().feedback(ss2.clone());
+        let ss_fb = ss1.clone().feedback(&ss2);
         let tf_fb = ss_fb.to_tf().unwrap();
         assert_abs_diff_eq!(tf_fb, Tf::s() / (Tf::s() + 2.0));
 
         let ss2 = Ss::<Continuous>::new_from_scalar(1.0);
-        let ss_fb = ss1.clone().feedback(ss2.clone());
+        let ss_fb = ss1.clone().feedback(&ss2);
         let tf_fb = ss_fb.to_tf().unwrap();
         assert_abs_diff_eq!(tf_fb, 0.5 * Tf::s() / (Tf::s() + 0.5));
 
@@ -989,7 +989,7 @@ mod tests {
             let ss1 = tf1.to_ss_method(ControllableCF).unwrap();
             let ss2 = tf2.to_ss_method(ObservableCF).unwrap();
 
-            let ss_fb = ss1.feedback(ss2);
+            let ss_fb = ss1.feedback(&ss2);
             let ss_fb = ss_fb.to_tf().unwrap();
             let tf_fb = tf1.feedback(&tf2);