Why isn't the hold on feature working? It only shows my last plot.

figure();
plot(ans.p_controller, 'b')
hold on
plot(ans.pd_controller, 'r')
plot(ans.pi_controller, 'g')
plot(ans.pid_controller, 'k')
hold off
xlabel('Time (sec)')
ylabel('Rotation (Degrees)')
legend('P Controller', 'PD Controller', 'PI Controller', 'PID Controller')
title('Closed Loop Controllers')
grid on

[Walter Roberson]

1. Possibly the other data is all NaN or inf
2. Possibly the other data is the same as the last data, so the last plot is exactly on top of the other plots.

Answer 1

[Image Analyst]

How did you get "ans"? ans is a reserved keyword that gets changed very frequently, like when you call a function without accepting any return arguments. You should NEVER use it as the name of your variable. Calling plot without any return argument will return the handle to the plot in ans, thus overwriting whatever you had in ans. Each call to plot will overwrite ans.

Please call your "ans" variable by another name and then try it. It should work.

help plot

 plot - 2-D line plot
    This MATLAB function creates a 2-D line plot of the data in Y versus the
    corresponding values in X.

    Vector and Matrix Data
      plot(X,Y)
      plot(X,Y,LineSpec)
      plot(X1,Y1,...,Xn,Yn)
      plot(X1,Y1,LineSpec1,...,Xn,Yn,LineSpecn)
      plot(Y)
      plot(Y,LineSpec)

    Table Data
      plot(tbl,xvar,yvar)
      plot(tbl,yvar)

    Additional Options
      plot(ax,___)
      plot(___,Name,Value)
      p = plot(___)

    Input Arguments
      X - x-coordinates
        scalar | vector | matrix
      Y - y-coordinates
        scalar | vector | matrix
      LineSpec - Line style, marker, and color
        string scalar | character vector
      tbl - Source table
        table | timetable
      xvar - Table variables containing x-coordinates
        string array | character vector | cell array | pattern |
        numeric scalar or vector | logical vector | vartype()
      yvar - Table variables containing y-coordinates
        string array | character vector | cell array | pattern |
        numeric scalar or vector | logical vector | vartype()
      ax - Target axes
        Axes object | PolarAxes object | GeographicAxes object

    Name-Value Arguments
      Color - Line color
        [0 0.4470 0.7410] (default) | RGB triplet | hexadecimal color code |
        "r" | "g" | "b" | ...
      LineStyle - Line style
        "-" (default) | "--" | ":" | "-." | "none"
      LineWidth - Line width
        0.5 (default) | positive value
      Marker - Marker symbol
        "none" (default) | "o" | "+" | "*" | "." | ...
      MarkerIndices - Indices of data points at which to display markers
        1:length(YData) (default) | vector of positive integers |
        scalar positive integer
      MarkerEdgeColor - Marker outline color
        "auto" (default) | RGB triplet | hexadecimal color code | "r" |
        "g" | "b" | ...
      MarkerFaceColor - Marker fill color
        "none" (default) | "auto" | RGB triplet | hexadecimal color code |
        "r" | "g" | "b" | ...
      MarkerSize - Marker size
        6 (default) | positive value
      DatetimeTickFormat - Format for datetime tick labels
        character vector | string
      DurationTickFormat - Format for duration tick labels
        character vector | string

    Examples
      openExample('graphics/CreateLinePlotExample')
      openExample('graphics/PlotMultipleLinesExample')
      openExample('graphics/CreateLinePlotFromMatrixExample')
      openExample('graphics/SpecifyLineStyleExample')
      openExample('graphics/SpecifyLineStyleColorAndMarkerExample')
      openExample('graphics/DisplayMarkersAtSpecificDataPointsExample')
      openExample('graphics/SpecifyLineWidthMarkerSizeAndMarkerColorExample')
      openExample('graphics/AddTitleAndAxisLabelsExample')
      openExample('matlab/SpecifyDurationTickFormatsExample')
      openExample('graphics/PlotTableDataExample')
      openExample('graphics/PlotTableMutliVariablesExample')
      openExample('graphics/PlotSpecifyAxes19bExample')
      openExample('graphics2/ChangeLinePropertiesUsingHandlesExample')
      openExample('graphics/PlotCircleExample')

    See also title, xlabel, ylabel, xlim, ylim, legend, hold, gca, yyaxis,
      plot3, loglog, Line Properties

    Introduced in MATLAB before R2006a
    Documentation for plot
       doc plot

    Other uses of plot

       AggregateBayesianOptimization/plot
       alphaShape/plot
       antenna.Circle/plot
       backscatterBicyclist/plot
       backscatterPedestrian/plot
       Battery.Parameters/plot
       Battery.Pulse/plot
       Battery.PulseSequence/plot
       BayesianOptimization/plot
       blm/plot
       cfit/plot
       cgdatasetnode/plot
       cgrules/plot
       cgv.CGV/plot
       clusterDBSCAN/plot
       clustergram/plot
       clustering.evaluation.CalinskiHarabaszEvaluation/plot
       comm.MemorylessNonlinearity/plot
       comm.Ray/plot
       conjugateblm/plot
       cornerPoints/plot
       customblm/plot
       cylinderModel/plot
       DataMatrix/plot
       diffuseblm/plot
       digraph/plot
       driving.heremaps.LaneTopology/plot
       driving.Path/plot
       drivingScenario/plot
       dtree/plot
       empiricalblm/plot
       esbacktest/plot
       eyeMask/plot
       fairnessMetrics/plot
       frd/plot
       graph/plot
       HeatMap/plot
       iddata/plot
       idnlarx/plot
       idnlhw/plot
       imageviewset/plot
       InflationCollisionChecker/plot
       KAZEPoints/plot
       laneBoundarySegment/plot
       lassoblm/plot
       LayerGraph/plot
       LeastSquaresResults/plot
       lidarScan/plot
       lime/plot
       LinearModel/plot
       localavfit/plot
       localmod/plot
       localmulti/plot
       matlab.buildtool.Plan/plot
       mixconjugateblm/plot
       mixsemiconjugateblm/plot
       monovslam/plot
       mpc/plot
       MSERRegions/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
       pulseWaveformLibrary/plot
       reidentificationmetrics/plot
       RepeatedMeasuresModel/plot
       rfchain/plot
       rgbdvslam/plot
       roadrunnerHDMap/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
       stereovslam/plot
       sweepset/plot
       tall/plot
       timeseries/plot
       tireData/plot
       tireModel/plot
       trajectoryErrorMetrics/plot
       umargin/plot
       varbacktest/plot
       vehicleCostmap/plot
       wdectree/plot
       xregmodel/plot
       xregtransient/plot
       xregtwostage/plot

[Walter Roberson]

Calling plot without any return argument will return the handle to the plot in ans

That turns out not to be the case.

123

ans = 123

ans

ans = 123

plot(1:5)

ans

ans = 123

[Image Analyst]

OK, that seems unexpected and inconsistent with most/all of the other functions that return their value in ans if you don't explicitly accept it into a named variable. Well anyway, it's not good to have variables of your own named ans.

[埃博拉酱]

@Image Analyst Some functions check for nargout. If it is 0, it does not produce a return value to improve performance.