# Dynamic ## Implicit Dynamics System The implicit dynamics system uses displacement as the primary variable. ### Syntax ``` step dynamic (1) (2) step implicitdynamic (1) (2) # (1) int, unique step tag # (2) double, step size ``` ### Remarks 1. Displacement control solver [`MPDC`](https://tlcfem.gitbook.io/suanpan-manual/solver/mpdc) is automatically enabled if a displacement load is active. 2. The [`Newmark`](https://tlcfem.gitbook.io/suanpan-manual/integrator/implicit/newmark/newmark) is automatically enabled if there is no valid integrator defined. ## Explicit Dynamics System The explicit dynamics system uses acceleration as the primary variable. All displacement based loads/constraints cannot be not applied. ### Syntax ``` step explicitdynamic (1) (2) # (1) int, unique step tag # (2) double, step size ``` ### Remarks 1. The [`Tchamwa`](https://tlcfem.gitbook.io/suanpan-manual/integrator/explicit/tchamwa) with spectral radius of $$0.8$$ is automatically enabled if there is no valid integrator defined. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://tlcfem.gitbook.io/suanpan-manual/step/dynamic.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.