How to set the fixed start and enf od the axis value?

[wang9658]

I want to get an axis like this:
1.jpg

The axis from 20-20K.
between 20 and 100, the step is 10
between 100-1K, the step is 100
between 1K-10K, the step is 1000
and 10K-20K, the step is 10k.

I copy some code from qwt example,like the following:

logSpace(frequency, 20000, 20,20000);
...
currentCurve->setSamples(frequency, amplitude, 20000);
...
#define qExp(x) ::exp(x)
#define qAtan2(y, x) ::atan2(y, x)
 
static void logSpace( double *array, int size, double xmin, double xmax )
{
    if ( ( xmin <= 0.0 ) || ( xmax <= 0.0 ) || ( size <= 0 ) )
        return;
 
    const int imax = size - 1;
 
    array[0] = xmin;
    array[imax] = xmax;
 
    const double lxmin = log( xmin );
    const double lxmax = log( xmax );
    const double lstep = ( lxmax - lxmin ) / double( imax );
 
    for ( int i = 1; i < imax; i++ )
        array[i] = qExp( lxmin + double( i ) * lstep );
}

logSpace(frequency, 20000, 20,20000);
...
currentCurve->setSamples(frequency, amplitude, 20000);
...
#define qExp(x) ::exp(x)
#define qAtan2(y, x) ::atan2(y, x)

static void logSpace( double *array, int size, double xmin, double xmax )
{
    if ( ( xmin <= 0.0 ) || ( xmax <= 0.0 ) || ( size <= 0 ) )
        return;

    const int imax = size - 1;

    array[0] = xmin;
    array[imax] = xmax;

    const double lxmin = log( xmin );
    const double lxmax = log( xmax );
    const double lstep = ( lxmax - lxmin ) / double( imax );

    for ( int i = 1; i < imax; i++ )
        array[i] = qExp( lxmin + double( i ) * lstep );
}

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But I got the following display:
2.PNG
, it's not from 20-20k. changed to 10-100k.

What I can do?