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Student Support Forum > General > > "Coupled Differential Solving"

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Original Message (ID '128298') By Bill Simpson:
In your notebook The first problem you have is using {} instead of (). Those are completely different and cannot be substituted for each other. {} are used ONLY to enclose lists of items. () are used ONLY to control precedence and order of operations. Using Magnification to blow up the size of the notebook can make it easier to spot these mistakes. The second problem you have is the initial conditions. You have both y'[0]==1 and y'[0]== -1. You also only have two first order differential equations but four initial conditions. Even if I eliminate your y'[0] conditions I still get warnings about non-numerical values at t==0. The third problem is that you are using a range {t,1} for NDSolve and it requires {t,low,high}. Even when I subsititute {t,1,10} I still have the complaint about non-numerical values. The fourth problem is that NDSolve requires every variable to have an explicit numerical value unless it is the function you are solving for or the independent variable. You have v, vm, icn that have not been assigned constant numeric values. It isn't happy about your a or b either. If you can fix all those then you should be much closer to a solution and we can try to work on the next layer of problems.