René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Should outputs that are continuous states be dependent on themselves?","articleBody":"Yes, this is about states being outputs. Again.\n\n(Maybe this is also a question for the specification)\n\nTake e.g., the VanDerPol example, FMI3, both continuous states are also (the only) outputs.\n\nIn the state-space representation, this makes the \"C\" matrix the identity. The issues are that:\n\n1. The structure of the \"C\" matrix is not reflected by the dependencies of the outputs.\n2. Using only `directional_derivatives` to obtain the \"C\" matrix actually yields the wrong result.\n\nSure, all the information that the outputs are in fact also states is contained in the `modelDescription.xml` and an importer can use it to generate the correct state space matrices. So, one could argue this is a \"quality of implementation\" thing. \n\nOne may also argue that e.g., `output_1 = x0` has a constant dependency on `x0` i.e., the current dependencies are wrong.\n\nEither way, one could also make it easier on the importers here and add the dependencies + have the directional derivatives of (output) states with respect to themselves to be 1.\n\n\n\nFrom the specification point of view, this seems somewhat like an edge case... ? Based on https://fmi-standard.org/docs/3.0/#ModelStructure -\u003e Table 24:\n\n```\nKnowns vknown\n in Event Mode and Continuous-Time Mode (ME) and at communication points (CS and SE) for Output and ContinuousStateDerivative elements are:\n\n-[...]\n- continuous states and discrete-time states,\n```\n\nSo, an output double acting as continuous state is both an unknown and known. \n\n\nAny thoughts/input welcome.\n\n/Peter","author":{"url":"https://github.com/PeterMeisrimelModelon","@type":"Person","name":"PeterMeisrimelModelon"},"datePublished":"2025-07-23T12:28:44.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/657/Reference-FMUs/issues/657"}