add 3pt quadratic minimization function

modules/util/util.py

@@ -108,4 +108,11 @@ def pressure_to_altitude(pres, temp, prof_pres, prof_temp, sfc_pres, sfc_temp, s
 
     z = thickness_hydrostatic(prof_pres, prof_temp) + sfc_elev
 
-    return z
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+    return z
+
+
+# http://fourier.eng.hmc.edu/e176/lectures/NM/node25.html
+def minimize_quadratic(xa, xb, xc, ya, yb, yc):
+    x_min = xb + 0.5*(((ya-yb)*(xc-xb)*(xc-xb) - (yc-yb)*(xb-xa)(xb-xa)) /
+                      ((ya-yb)*(xc-xb) + (yc-yb)*(xb-xa)))
+    return x_min
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