# Mischa Kim

### MathWorks

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Professional Interests: Spacecraft dynamics and control, numerical analysis, simulation, animation

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**Content Feed**

Properties of exponentials - symbolic algebra

Hi Luca, use syms x y z = simplify(exp(x)*exp(y))

plus d'un an ago | 0

how to make matlab functions work not starting at the first element

Hi Naufal, how about: a = [2 5 2 4 2 7 2 2 2 5 2]; pks = findpeaks(a); mypks = pks(2:end); To be able to skip the firs...

plus d'un an ago | 0

Question about plotting graph.

Hi, how about plot(T0,y,'ro') Since this is only one single data point it is hard to see in the plot, hence I change the color...

plus d'un an ago | 0

Problem in displaying or printing final result.

Hi Masoud, use fprintf instead. Check out the examples in the link.

plus d'un an ago | 1

| accepted

why didn't the event function detect the events?

In your ode45 call you are not returning any event information. Replace with [tout,yout,te,ye,ie] = ode45(@Tq_Tj,tspan, y0,opti...

plus d'un an ago | 0

Basins of attraction and Newtons Method.

One problem was in the governing equations for f. I cleaned up a bit and this works now: % Governing equations f = [-7.716*1e-...

plus d'un an ago | 0

Empty windows in EditFields of app.designer?

ErikJon, as a workaround you could use an Edit Field (Text) instead of Edit Field (Numeric). The drawback of this workaround is ...

plus d'un an ago | 0

| accepted

Getting extra parameters from ODE45 and the mystery transpose

Hi Simon, to your first question: When you assign values to dx(1), dx(2), and so on you are creating a row vector. However, you ...

plus d'un an ago | 0

| accepted

How to solve the error "[t, z]= ode45(@observer, t_temp,z0)" in line 23.

dzdt seems to be a (3x2 ?) matrix. It needs to be a 3x1 vector to be consistent with the initial conditions, z0, which is also a...

plus d'un an ago | 1

| accepted

Why am i receiving "Error:Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters."? for S(K)>0

Hi, since you do not know the number of iterations it makes more sense to use a while instead of a for loop: while S(K)>0 %as l...

plus d'un an ago | 1

| accepted

How to count the number of different strings in a string list?

Hi, use str = {'AAA','ABB','CDE','ABB','CCR','AAA','FDR'}; numstr = numel(unique(str))

plus d'un an ago | 0

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How to extract value at a given time in ode 45

Hi Shubham, use an events functions, see the example below. With events functions you can identify zero crossings; in your case ...

plus d'un an ago | 0

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Draw a circle on matlab app designer?

Hi ErikJon, if the plot input is a matrix (e.g. your circ) "...the plot function plots the columns of the matrix (circ) versus t...

plus d'un an ago | 0

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please help me (dsolve)

Use instead syms y(t) eqn = diff(y,t,2) + 0.5*diff(y,t) + y == 3; Dy = diff(y,t); cond = [y(0) == 0.5, Dy(0) == 0]; w ...

plus d'un an ago | 0

confusing ode suits for solving discontinuous odes

Hi, this is because the integrator, ode45, adjusts the integration step size. Broadly speaking where the dynamics is more comple...

plus d'un an ago | 0

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How to Find average value for every 10 sets of a matrix

Hi Magdy, you could use something like: x = 1:1:12; % this would be your matrix A y = reshape(x,3,4) m = mean(y,1)

plus d'un an ago | 0

| accepted

How to Use "Ask a Question" Section Correctly?

Hi Ercan, thanks for flagging this. I have seen the same behavior this morning in Chrome, other browsers seemed to work fine. I ...

plus d'un an ago | 3

| accepted

ODE Event Location detecting events other than zero

Hi Hariharan, yes it is. You simply define a function that is equal to zero whenever your expression equals a certain value. Fo...

plus d'un an ago | 0

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How do I change the values for x-axis ?

Hi Anne-Lise, do you mean changing the tick labels? See this answer. If this does not address your question, how exactly do you ...

plus d'un an ago | 1

Why is the resulting time-domain curve from Euler method and ode45 not stable?

Hi Ni Made Ayu Sinta Dewi, there is nothing you are doing wrong. What you are seeing is expected behavior. This is because you a...

plus d'un an ago | 0

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ode45 fail with pendulum

Hi Bobby, this is the wonderful world of numerical (vs symbolic) computation. ode45 is a numerical integrator that approximates ...

plus d'un an ago | 0

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Changing Length of Pendulum while it is in motion

Dear Yan Koon Ang, this is possible. In the example you are referring to in your question you would have to make the time varia...

plus d'un an ago | 1

I am trying to plot x and y with y being the only unknown but I don’t what is wrong in my code please help

Honore, the one thing I notice is that x and y are vectors. Rewrite the y-equation using the dot operator, .^ instead of just ...

plus d'un an ago | 0

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Finding the initial conditions which give a specified event using ode45

Patrick, as Walter pointed out this is a BVP. However, you can and I personally would use ode45 and the so-called shooting meth...

plus d'un an ago | 0

Differential equation by simulink

Double-klick on the integrator blocks and you'll see that the default initial condition is zero (0). It is also inside the integ...

plus d'un an ago | 0

when i run the code the plot graphs appears empty here is the code please help to find the mistake i made

Seif, I believe this is what you are trying to do: %calculating velocity V3 = 10; % velocity of the piston in cm/sec %global...

plus d'un an ago | 0

| accepted

How to change a Function by a Variable

Ercan, here you go, for the first term: syms phi x A B eq = A*sin(phi) + B*cos(phi) eq = subs(eq,sin(phi),2*x/(1+x^2))

plus d'un an ago | 1

| accepted

How to write Newton method with exact number of iterations and see all digit ? for example if method is required to take exact 5 iterations of newton's method

Add a loop index, e.g. ii. Also, you set your code as a function. This means you can call it, e.g., from the command window usin...

plus d'un an ago | 0

serie with two parameters

Sara, it really depends on what you are trying to achieve. For starters you could use two for loops to take care of the summatio...

plus d'un an ago | 0

Plotting a function with 2 dependent variables

Use meshgrid instead: [x,y] = meshgrid(-10:0.1:10); z = sin(x).*cos(y); plot3(x,y,z)

plus d'un an ago | 0