## Warnings on keywords when importing input file to ABAQUS

I want to analyze a steel frame with pin connections at both sides or one side at some beams. I found the keyword *Release is very useful and convenient, so I resort to this keyword. I wrote the input file with the same syntax rules, so that it will be more convenient for me to establish more models. However, when I try to run the input file, there are warnings and errors even with the input file generated from a

## Differential equation – Part I First-Order ODE

Euler equation: \left\{ \begin{align} & {{x}_{n+1}}={{x}_{n}}+h \\ & {{y}_{n+1}}={{y}_{n}}+{{A}_{n}}h \\ \end{align} \right. \left\{ \begin{align} & h=\text{step}\text{size} \\ & {{A}_{n}}=f\left( {{x}_{n}},{{y}_{n}} \right) \\ \end{align} \right. Error of solution error = exact solution – approximate solution Method 1: smaller step Euler first-order: $e\sim {{c}_{1}}h$, proportional to step size Method 2: find a better slop ${{A}_{n}}$ Heun’s method = improved Euler method = modified Euler method = RK2 \left\{ \begin{align} & {{x}_{n+1}}={{x}_{n}}+h \\ & {{y}_{n+1}}={{y}_{n}}+h\left( \frac{{{A}_{n}}+{{B}_{n}}}{2} \right) \\ \end{align} \right. in which, \({{B}_{n}}=f\left(

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