Help with android math problem

Question

1.80/5 (2 votes)

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I am trying to get water flow with this formula but when I run my app I get 64.52 and I should get 92.71. If I run the same formula in vb.net it works fine. Can sum one please take a look and see what I'm not doing right.

P.S. I'm just starting to learn Android.

Thanks.

Android Code

C#

public void buttonOnClick6(View v) {

        try {

            double B1 = 4      //Double.parseDouble(((EditText)findViewById(R.id.editText7)).getText().toString());
            double Y1 = 3      //Double.parseDouble(((EditText)findViewById(R.id.editText8)).getText().toString());
            double Z1 = 2      //Double.parseDouble(((EditText)findViewById(R.id.editText9)).getText().toString());
            double N1 = 0.012  //Double.parseDouble(((EditText)findViewById(R.id.editText10)).getText().toString());
            double S1 = 0.0003 //Double.parseDouble(((EditText)findViewById(R.id.editText11)).getText().toString());

            double A1 = (B1 * Y1) + Z1 * pow(Y1, 2);//tbB * tbY;
            double P1 = B1 + (2 * Y1) * pow((1 + pow(Z1, 2)), 0.5);//tbB + (2 * tbY);
            double R1 = A1 / P1;

            double CFS = ((1.49 / N1) * A1 * pow(R1, (2/3)) * pow(S1, 0.5));
            double SEC1 = (CFS / A1);

            TextView textElement3 = (TextView) findViewById(R.id.tb006);
            textElement3.setText("Cross-Sect. Area, A = " + String.format("%.2f",A1));

            TextView textElement4 = (TextView) findViewById(R.id.tb007);
            textElement4.setText("Wetted Perimeter, P = " + String.format("%.2f",P1));

            TextView textElement5 = (TextView) findViewById(R.id.tb008);
            textElement5.setText("Hydraulic Radius, R = " + String.format("%.2f",R1));

            TextView textElement1 = (TextView) findViewById(R.id.tbCFS1);
            textElement1.setText("CFS: " + String.format("%.2f",CFS));

            TextView textElement2 = (TextView) findViewById(R.id.tbSEC1);
            textElement2.setText("FT/SEC: " + String.format("%.3f",SEC1));

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

VB.NET Code this work fine

VB

Dim tbB1 As Double = 4
Dim tbY1 As Double = 3
Dim tbZ1 As Double = 2
Dim tbN1 As Double = 0.012
Dim tbS1 As Double = 0.0003

Dim A1 As Double = (tbB1 * tbY1) + tbZ1 * Pow(tbY1, 2)
Dim P1 As Double = tbB1 + (2 * tbY1) * Pow((1 + Pow(tbZ1, 2)), 0.5)
Dim R1 As Double = A1 / P1

Dim CFS1 As Double = (1.49 / tbN1) * A1 * Pow(R1, (2 / 3)) * Pow(tbS1, 0.5)
Dim FT_SEC1 As Double = CFS1 / A1

lbA.Content = "Cross-Sect. Area, A = " & A1
lbP.Content = "Wetted Perimeter, P = " & P1
lbR.Content = "Hydraulic Radius, R = " & R1

lbCFS.Content = "CFS: " & CFS1
lbFTSEC.Content = "FT/SEC: " & FT_SEC1

Posted 18-Feb-15 5:22am

strings11

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Comments

[no name] 18-Feb-15 11:29am

I don't know android, but my first Suggestion is: Whenever you use a double number write it as a double to avoid side effects. E.g. instead of Pow(R1, (2/3)) write Pow (R1, 2.0/3.0). This because I think to remember the the first one -depending on the language/environement- always means Pow(R1,0)....
Bruno

Sergey Alexandrovich Kryukov 18-Feb-15 11:34am

Use the debugger. Even if you want to get 42.
Look at the previous comment. 2/3 computes to 0.
—SA

phil.o 18-Feb-15 11:38am

Without having read other comments, I would also have gone for a problem with the 2 / 3 integer divison leading to zero.

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User 11060979 · Accepted Answer · 2015-02-18T06:29:00

Encouraged by the comments of SA and phil.o, I try to give an answer.

Write any double constant as double, means don't write x= 4, better use x= 4.0.

Some notes besides:
a.) Try to reduce the useless use of "()" where it is not needed. Multiplication before Addition is still valid ;)
b.) Pow(5, 2/3) vs. Pow(5, 2.0/3.0) you can easy check the difference in VS c#
Bruno