[Octave-bug-tracker] [bug #60239] Differential equations with initial conditions sometimes return wrong result

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?60239>

                 Summary: Differential equations with initial conditions
sometimes return wrong result
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Mon 15 Mar 2021 07:02:51 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: 6.2.0
         Discussion Lock: Any
        Operating System: Any

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Details:

syms y1 y2 M

DE1 = diff(diff(y1)) == -2*y1+y2
DE2 = diff(diff(y2)) == -2*y2+y1


DE = [DE1 DE2]
s = dsolve(DE,diff(y1)(0)==0,diff(y2)(0)==0,y1(0)==M,y2(0)==-M)
s{1}

// constant C_4 is not replaced by M/2
// the correct result is that C_4 = C_3
// s{1} is expected to be shown as M*cos(sqrt(3)*x)





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