# User Portlet

Discussions |
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I used implicit Euler and fixed step size to solve the differential equation, but the system prompted that "FixedStep" cannot be used. What is the reason for this and how should I modify the program? system = {vi q[t] == l il'[t] + ir[t] r,... |

I want to know the information about the **protectedSignalcurrent** component in Systemmodeler, but when I opened its documentation through "*View Class Documentation*", no information was displayed. I would like to know the characteristics of this... |

Yes, I found the help document for > **$MaxPickewiseCases** and directly set *$MaxPickewiseCases=(the range you want)*. The link to the help document is[enter link description here][1] But my code doesn't produce any results... ... |

*q[t]* is a switching function, and I want to mark the corresponding time point when the value of *q[t]* changes from 1 to 0 in the curve. How should I rewrite my code? (From the code, it can be seen that when Mod [t, \ [Tau]]=(2/3) \ [Tau], *q[t]*... |

May I ask if Mathematica provides a trapezoidal method instruction for solving differential equations? I checked the reference materials and for *NDSolve*, it seems that only explicit Euler, implicit Euler, midpoint method, etc. are provided, but it... |

The **SystemModelLinearize** instruction cannot be linearized properly, what is the reason for the following error after execution? ![enter image description here][1] model = ImportString[ "model Circuit\n parameter... |

Can I use **Log** instead of **MatrixLog**? Because I want to process vectors...... |

I think so, because I need to use the relationship between *t* and *dt* in the future. I have an idea, if **MatrixLog** cannot handle vectors, can I find the relationship between the **MatrixLog** and the **Log** in MMA, and then use **Log** instead... |

Okay, haha, what if I write it like this? {r = 22, l = 2 10^-1, c = 1 10^-4, vi = 24}; \[CapitalDelta]vi = 0; A = {{0, -1/l}, {1/c, -1/(r c)}}; G = Inverse[A]; B = {1/l, 0}; S1 = Inverse[DiagonalMatrix[{1, 1}] - dt*A +... |

condequal = Abs[ilerror] == error; dilt = D[condequal, t]; Solve[{condequal, dilt}, {t, dt}] Yes, it seems that after modifying to the above code, **Solve** cannot solve either. ![enter image description here][1] What if I want to... |