2.7E: Euler’s Method (Exercises)

Q3.1.1

You may want to save the results of these exercises, since we will revisit in the next two sections. In Exercises 3.1.1-3.1.5 use Euler’s method to find approximate values of the solution of the given initial value problem at the points \(x_i=x_0+ih\), where \(x_0\) is the point where the initial condition is imposed and \(i=1\), \(2\), \(3\). The purpose of these exercises is to familiarize you with the computational procedure of Euler’s method.

1. \(y'=2x^2+3y^2-2,\quad y(2)=1;\quad h=0.05\)

2. \(y'=y+\sqrt{x^2+y^2},\quad y(0)=1;\quad h=0.1\)

3. \(y'+3y=x^2-3xy+y^2,\quad y(0)=2;\quad h=0.05\)

4. \(y'= {1+x\over1-y^2},\quad y(2)=3;\quad h=0.1\)

5. \(y'+x^2y=\sin xy,\quad y(1)=\pi;\quad h=0.2\)

Q3.1.2

6. Use Euler’s method with step sizes \(h=0.1\), \(h=0.05\), and \(h=0.025\) to find approximate values of the solution of the initial value problem \[y'+3y=7e^{4x},\quad y(0)=2\] at \(x=0\), \(0.1\), \(0.2\), \(0.3\), …, \(1.0\). Compare these approximate values with the values of the exact solution \(y=e^{4x}+e^{-3x}\), which can be obtained by the method of Section 2.1. Present your results in a table like Table 3.1.1.

7. Use Euler’s method with step sizes \(h=0.1\), \(h=0.05\), and \(h=0.025\) to find approximate values of the solution of the initial value problem \[y'+{2\over x}y={3\over x^3}+1,\quad y(1)=1\] at \(x=1.0\), \(1.1\), \(1.2\), \(1.3\), …, \(2.0\). Compare these approximate values with the values of the exact solution \[y={1\over3x^2}(9\ln x+x^3+2),\] which can be obtained by the method of Section 2.1. Present your results in a table like Table 3.1.1.

8. Use Euler’s method with step sizes \(h=0.05\), \(h=0.025\), and \(h=0.0125\) to find approximate values of the solution of the initial value problem \[y'={y^2+xy-x^2\over x^2},\quad y(1)=2\] at \(x=1.0\), \(1.05\), \(1.10\), \(1.15\), …, \(1.5\). Compare these approximate values with the values of the exact solution \[y={x(1+x^2/3)\over1-x^2/3}\] obtained in Example [example:2.4.3}. Present your results in a table like Table 3.1.1.

9. In Example [example:2.2.3} it was shown that \[y^5+y=x^2+x-4\] is an implicit solution of the initial value problem \[y'={2x+1\over5y^4+1},\quad y(2)=1. \tag{A}\] Use Euler’s method with step sizes \(h=0.1\), \(h=0.05\), and \(h=0.025\) to find approximate values of the solution of (A) at \(x=2.0\), \(2.1\), \(2.2\), \(2.3\), …, \(3.0\). Present your results in tabular form. To check the error in these approximate values, construct another table of values of the residual \[R(x,y)=y^5+y-x^2-x+4\] for each value of \((x,y)\) appearing in the first table.

10. You can see from Example 2.5.1 that \[x^4y^3+x^2y^5+2xy=4\] is an implicit solution of the initial value problem \[y'=-{4x^3y^3+2xy^5+2y\over3x^4y^2+5x^2y^4+2x},\quad y(1)=1. \tag{A}\] Use Euler’s method with step sizes \(h=0.1\), \(h=0.05\), and \(h=0.025\) to find approximate values of the solution of (A) at \(x=1.0\), \(1.1\), \(1.2\), \(1.3\), …, \(2.0\). Present your results in tabular form. To check the error in these approximate values, construct another table of values of the residual \[R(x,y)=x^4y^3+x^2y^5+2xy-4\] for each value of \((x,y)\) appearing in the first table.

11. Use Euler’s method with step sizes \(h=0.1\), \(h=0.05\), and \(h=0.025\) to find approximate values of the solution of the initial value problem \[(3y^2+4y)y'+2x+\cos x=0, \quad y(0)=1; \quad\text{(Exercise 2.2.13)}\] at \(x=0\), \(0.1\), \(0.2\), \(0.3\), …, \(1.0\).

12. Use Euler’s method with step sizes \(h=0.1\), \(h=0.05\), and \(h=0.025\) to find approximate values of the solution of the initial value problem \[y'+{(y+1)(y-1)(y-2)\over x+1}=0, \quad y(1)=0 \quad\text{(Exercise 2.2.14)}\] at \(x=1.0\), \(1.1\), \(1.2\), \(1.3\), …, \(2.0\).