MATLAB: How to use str2func to replace eval command

evalstr2func

I want user to enter a parametrized function in terms of t. Is there a way that I can have an input function instead of using '' and eval?

t = linspace(0.001,2,1000);
T = t;
x_e = 't.^3';
y_e = 'exp(t)';
z_e = 'cos(10*t)';
x = eval(x_e);
y = eval(y_e);
z = eval(z_e);

Best Answer

fx = str2func(['@(t) ', x_e]);
x = fx(t);

Just like the examples in http://www.mathworks.com/help/matlab/ref/str2func.html

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MATLAB: How to get a derivated function df/dt

In R2015a, I get this result:

syms x(t) y(t) z(t)
z(t)=cos(x(t))+y(t)^2;
dzdt = diff(z, t)
dzdt(t) =
2*y(t)*diff(y(t), t) - sin(x(t))*diff(x(t), t)

MATLAB: Plotting the tragectory in MATLAB

In your Gravity function you have some variable name inconsistencies. E.g.,

function  dRV = Gravity(t, RV)
global T X_J Y_J Z_J X_M Y_M Z_M X_E Y_E Z_E mu_E mu_M mu_J mu_S
X = R(1);
Y = R(2);
Z = R(3);
VX = R(4);
VY = R(5);
VZ = R(6);
    :
dR(1) = VX
dR(2) = VY
dR(3) = VZ
dR(4) = dV * X
dR(5) = dV * Y
dR(6) = dV * Z

So, you pass in a variable named RV, but then access it using the variable name R. And your output variable is named dRV in the function line, but you use the name dR in your code. You need to pick consistent variable naming for these.

Best Answer

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MATLAB: How to get a derivated function df/dt

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