How do i get my answer to print into a table format instead of a single line

Hello,

I am trying to code to have data taken from a file and then transcribed into a new one. The process is working fine except i cannot get the code to print onto the new file in a table format that looks like the top one

The file im given the values from looks like

20    200  
30    250
25    300
20    400

My code looks like this

data=load('Lab3Problem2.txt');
%set matrix for newtons
N=data(:,1);
%set matrix for spring constant
k=data(:,2);
%find length using x=N/k
len_N=length(N);
x=zeros(len_N,1);
%create the Length array
for i = 1:len_N
    x(i)=N(i)/k(i)
end
E=zeros(len_N,1);
for i=1:len_N
    E(i)=(k(i)*x(i).^2)/2;
end
%write the data to answers txt file
fid=fopen('Springsanswers','wt');
fprintf(fid,'Spring1 Spring2 Spring3 Spring4');
fprintf(fid,'Force(N) %10d %10d %10d %10d',N');
fprintf(fid,'Spring Constant(N/m) %10d %10d %10d %10d',k');
fprintf(fid,'Potential energy(J) %10f %10f %10f %10f',E');
fclose(fid);

The solves the questions correctly however it displays the answer like this

Spring1 Spring2 Spring3 Spring4Force(N) 20 30 25 20Spring Constant(N/m) 200 250 300 400Potential energy(J) 1.000000 1.800000 1.041667 0.500000

Which is all in one row and not the way that is being required.

Any help would be appreciated!

Answer 1

[Star Strider]

Your code is close. Use tab characters ('\t') and carriage return-newline ('\n') characters as appropriate:

fprintf(fid,'\t\t\t\t\t\t\tSpring1\t\tSpring2\t\tSpring3\t\tSpring4\n');
fprintf(fid,'Force(N)\t\t\t\t%10d\t%10d\t%10d\t%10d\n',N');
fprintf(fid,'Spring Constant(N/m)\t%10d\t%10d\t%10d\t%10d\n',k');
fprintf(fid,'Potential energy(J)\t\t%10f\t%10f\t%10f\t%10f\n',E');

See the documentation on fprintf completely to understand all the interesting possibilities it has to offer.

[dpb]

Or, since you've solved the problem on your own, aren't giving anything away -- you could use a table in the end and MATLAB matrix operations --

k=data(:,2);
N=data(:,1);
x=N./k;
E=k.*x.^2/2;
t=array2table([N k x E].','VariableNames',compose('Spring%d',1:4));
t.Properties.RowNames={'Force(N)','Spring Constant(N/m)','Extension(m)','Potential Energy(J)'}

results in

t =
  4×4 table
                            Spring1    Spring2    Spring3     Spring4
                            _______    _______    ________    _______
    Force(N)                   20         30            25       20  
    Spring Constant(N/m)      200        250           300      400  
    Extension(m)              0.1       0.12      0.083333     0.05  
    Potential Energy(J)         1        1.8        1.0417      0.5  
>> 

You don't have the freedom to set a fixed format string for each variable this way, but it illustrates a very nice feature of the MATLAB table class that comes along for the ride -- legible formatting in the command window.

[dpb]

Alternatively, if it is required to write to a file, something like

fmt1=['%20s' repmat('%10s',1,4) '\n'];
fmt2=['%20s' repmat('%10g',1,4) '\n'];
fprintf(fmt1,blanks(4),t.Properties.VariableNames{:})
for i=1:4
  fprintf(fmt2,t.Properties.RowNames{i},t{i,:})
end

yields

                       Spring1   Spring2   Spring3   Spring4
            Force(N)        20        30        25        20
Spring Constant(N/m)       200       250       300       400
        Extension(m)       0.1      0.12 0.0833333      0.05
 Potential Energy(J)         1       1.8   1.04167       0.5

One can futz with the above to set format strings for specific formats; the '%g' for numeric uses 6 significant digits by default; using the width field lets you align things more easily than counting tabs.

Unfortunately, TMW chose the C formatting rules/io instead of Fortran FORMAT which is much easier to write as it supports repeat field counts, etc., etc., that have to do manually/explicitly in C.

ADDENDUM:

" the '%g' for numeric" you will notice exactly reproduces the precision of the table output; only TMW got a little more clever in defining column heading spacing to center on the output columns instead of just using same fixed spacing as did I.

[Steven Lord]

If you have a table array you want to write to a file, see writetable.

[dpb]

Being homework, I figured writetable was probably off the table... :)