simple x.y plot

%Q2) Create a variable 𝑥 which is a vector containing multiples of 5 between 
% 0 and 50.
x = (0:5:50)
% Compute the function 𝑦 and plot it against 𝑥 using red colour dash line 
% with circle markers:
y = (4*(x^2)*log(6))+(5*(x^2)) / sqrt (cos(x).^2) +1 
plot (x,y, r--o)

[VBBV]

Markers inside the plot function are accessed using strtings/chars

%Q2) Create a variable 𝑥 which is a vector containing multiples of 5 between 
% 0 and 50.
x = (0:5:50);
% Compute the function 𝑦 and plot it against 𝑥 using red colour dash line 
% with circle markers:
y = ((4*(x.^2)*log(6))+(5*(x.^2))) ./ (sqrt (cos(x).^2)+1 );
plot (x,y, '--ro')  % remember markers are accessed using strings/chars

Matlab intreprets any text placed outisde the chars/strings as variables of other data types and expects input values to those variables.

help plot

 PLOT   Linear plot. 
    PLOT(X,Y) plots vector Y versus vector X. If X or Y is a matrix,
    then the vector is plotted versus the rows or columns of the matrix,
    whichever line up.  If X is a scalar and Y is a vector, disconnected
    line objects are created and plotted as discrete points vertically at
    X.
 
    PLOT(Y) plots the columns of Y versus their index.
    If Y is complex, PLOT(Y) is equivalent to PLOT(real(Y),imag(Y)).
    In all other uses of PLOT, the imaginary part is ignored.
 
    Various line types, plot symbols and colors may be obtained with
    PLOT(X,Y,S) where S is a character string made from one element
    from any or all the following 3 columns:
 
           b     blue          .     point              -     solid
           g     green         o     circle             :     dotted
           r     red           x     x-mark             -.    dashdot 
           c     cyan          +     plus               --    dashed   
           m     magenta       *     star             (none)  no line
           y     yellow        s     square
           k     black         d     diamond
           w     white         v     triangle (down)
                               ^     triangle (up)
                               <     triangle (left)
                               >     triangle (right)
                               p     pentagram
                               h     hexagram
                          
    For example, PLOT(X,Y,'c+:') plots a cyan dotted line with a plus 
    at each data point; PLOT(X,Y,'bd') plots blue diamond at each data 
    point but does not draw any line.
 
    PLOT(TBL,XVAR,YVAR) plots the variables xvar and yvar from the table
    tbl. To plot one data set, specify one variable for xvar and one
    variable for yvar. To plot multiple data sets, specify multiple
    variables for xvar, yvar, or both. If both arguments specify multiple
    variables, they must specify the same number of variables
  
    PLOT(TBL,YVAR) plots the specified variable from the table against the
    row indices in the table. If the table is a timetable, the specified
    variable is plotted against the row times from the timetable.
 
    PLOT(X1,Y1,S1,X2,Y2,S2,X3,Y3,S3,...) combines the plots defined by
    the (X,Y,S) triples, where the X's and Y's are vectors or matrices 
    and the S's are strings.  
 
    For example, PLOT(X,Y,'y-',X,Y,'go') plots the data twice, with a
    solid yellow line interpolating green circles at the data points.
 
    The PLOT command, if no color is specified, makes automatic use of
    the colors specified by the axes ColorOrder property.  By default,
    PLOT cycles through the colors in the ColorOrder property.  For
    monochrome systems, PLOT cycles over the axes LineStyleOrder property.
 
    Note that RGB colors in the ColorOrder property may differ from
    similarly-named colors in the (X,Y,S) triples.  For example, the 
    second axes ColorOrder property is medium green with RGB [0 .5 0],
    while PLOT(X,Y,'g') plots a green line with RGB [0 1 0].
 
    If you do not specify a marker type, PLOT uses no marker. 
    If you do not specify a line style, PLOT uses a solid line.
 
    PLOT(AX,...) plots into the axes with handle AX.
 
    PLOT returns a column vector of handles to lineseries objects, one
    handle per plotted line. 
 
    The X,Y pairs, or X,Y,S triples, can be followed by 
    parameter/value pairs to specify additional properties 
    of the lines. For example, PLOT(X,Y,'LineWidth',2,'Color',[.6 0 0]) 
    will create a plot with a dark red line width of 2 points.
 
    Example
       x = -pi:pi/10:pi;
       y = tan(sin(x)) - sin(tan(x));
       plot(x,y,'--rs','LineWidth',2,...
                       'MarkerEdgeColor','k',...
                       'MarkerFaceColor','g',...
                       'MarkerSize',10)
 
    See also TITLE, XLABEL, YLABEL, XLIM, YLIM, LEGEND, HOLD, GCA, YYAXIS,
    PLOT3, SEMILOGX, SEMILOGY, LOGLOG, TILEDLAYOUT, HOLD, LEGEND, SCATTER

    Documentation for plot
       doc plot

    Other uses of plot

       alphaShape/plot
       antenna/plot
       Battery.Parameters/plot
       Battery.Pulse/plot
       Battery.PulseSequence/plot
       BayesianOptimization/plot
       blm/plot
       cfit/plot
       cgv.CGV/plot
       clustergram/plot
       clustering.evaluation.CalinskiHarabaszEvaluation/plot
       comm.MemorylessNonlinearity/plot
       conjugateblm/plot
       cornerPoints/plot
       customblm/plot
       cylinderModel/plot
       diffuseblm/plot
       digraph/plot
       driving.heremaps.LaneTopology/plot
       driving.Path/plot
       drivingScenario/plot
       dspdata/plot
       dtree/plot
       empiricalblm/plot
       fairnessMetrics/plot
       frd/plot
       graph/plot
       HeatMap/plot
       iddata/plot
       idnlarx/plot
       idnlhw/plot
       imageviewset/plot
       InflationCollisionChecker/plot
       KAZEPoints/plot
       lassoblm/plot
       LayerGraph/plot
       LeastSquaresResults/plot
       lime/plot
       LinearModel/plot
       matlab.buildtool.Plan/plot
       mixconjugateblm/plot
       mixsemiconjugateblm/plot
       monovslam/plot
       mpc/plot
       MSERRegions/plot
       nav/plot
       NLMEResults/plot
       ntree/plot
       opc.hda.Data/plot
       opticalFlow/plot
       parkingSpace/plot
       pathPlannerRRT/plot
       pcviewset/plot
       phased.FMCWWaveform/plot
       phased.LinearFMWaveform/plot
       phased.MFSKWaveform/plot
       phased.PhaseCodedWaveform/plot
       phased.RectangularWaveform/plot
       phased.SteppedFMWaveform/plot
       phytree/plot
       polyshape/plot
       predmaint/plot
       prob.NormalDistribution/plot
       propagationData/plot
       quantumCircuit/plot
       RepeatedMeasuresModel/plot
       rfchain/plot
       roadrunnerHDMap/plot
       robotics/plot
       rocmetrics/plot
       semiconjugateblm/plot
       sfit/plot
       shapley/plot
       SimBiology.fit.ParameterConfidenceInterval/plot
       SimBiology.fit.PredictionConfidenceInterval/plot
       SimBiology.gsa.ElementaryEffects/plot
       SimBiology.gsa.MPGSA/plot
       SimBiology.gsa.Sobol/plot
       simscape.logging.Node/plot
       simscape.logging.Series/plot
       simscape.logging/plot
       Simulink.sdi.DatasetRef/plot
       Simulink.sdi/plot
       Simulink.SimulationData.Parameter/plot
       slrealtime.ProfilerData/plot
       tall/plot
       timeseries/plot
       tireData/plot
       tireModel/plot
       umargin/plot
       varbacktest/plot
       vehicleCostmap/plot
       wdectree/plot

Answer 1

[Torsten]

Use

y = (4*(x.^2)*log(6))+(5*(x.^2)) ./ sqrt (cos(x).^2) +1 

instead of

y = (4*(x^2)*log(6))+(5*(x^2)) / sqrt (cos(x).^2) +1

[Steven Lord]

Newer users tend to encounter this type of problem frequently as they start learning MATLAB. A couple releases ago (after 20 years I can't always remember offhand when we made certain changes :) I believe we enhanced the error message to try to provide more information about how to solve the problem.

%Q2) Create a variable 𝑥 which is a vector containing multiples of 5 between 
% 0 and 50.
x = (0:5:50)

x = 1x11

0 5 10 15 20 25 30 35 40 45 50

% Compute the function 𝑦 and plot it against 𝑥 using red colour dash line 
% with circle markers:
y = (4*(x^2)*log(6))+(5*(x^2)) / sqrt (cos(x).^2) +1 

Error using ^
Incorrect dimensions for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To operate on each element of the matrix individually, use POWER (.^) for elementwise power.

Is there any information you think could be added to this message or a way to rephrase some or all of it that would help users (especially newer users) to more effectively understand the problem and correct it themselves, without having to reach out to Answers or other MATLAB experts in their vicinity?

[Torsten]

Is there any information you think could be added to this message or a way to rephrase some or all of it that would help users (especially newer users) to more effectively understand the problem and correct it themselves, without having to reach out to Answers or other MATLAB experts in their vicinity?

Maybe by including a link to a documentation page where Array vs. Matrix Operations are explained in examples ?

Like here:

https://uk.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

?